Annotation of src/usr.bin/lex/flex.1, Revision 1.38
1.38 ! bentley 1: .\" $OpenBSD: flex.1,v 1.37 2014/03/23 16:28:29 jmc Exp $
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1.2 deraadt 5: .\"
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7: .\" Vern Paxson.
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1.16 jmc 31: .\"
1.38 ! bentley 32: .Dd $Mdocdate: March 23 2014 $
1.16 jmc 33: .Dt FLEX 1
34: .Os
35: .Sh NAME
36: .Nm flex
37: .Nd fast lexical analyzer generator
38: .Sh SYNOPSIS
39: .Nm
1.28 jmc 40: .Bk -words
1.31 jmc 41: .Op Fl 78BbdFfhIiLlnpsTtVvw+?
1.16 jmc 42: .Op Fl C Ns Op Cm aeFfmr
43: .Op Fl Fl help
44: .Op Fl Fl version
1.28 jmc 45: .Op Fl o Ns Ar output
46: .Op Fl P Ns Ar prefix
47: .Op Fl S Ns Ar skeleton
48: .Op Ar
49: .Ek
1.21 jmc 50: .Sh DESCRIPTION
51: .Nm
52: is a tool for generating
53: .Em scanners :
54: programs which recognize lexical patterns in text.
55: .Nm
56: reads the given input files, or its standard input if no file names are given,
57: for a description of a scanner to generate.
58: The description is in the form of pairs of regular expressions and C code,
59: called
60: .Em rules .
61: .Nm
62: generates as output a C source file,
63: .Pa lex.yy.c ,
64: which defines a routine
65: .Fn yylex .
66: This file is compiled and linked with the
67: .Fl lfl
68: library to produce an executable.
69: When the executable is run, it analyzes its input for occurrences
70: of the regular expressions.
71: Whenever it finds one, it executes the corresponding C code.
72: .Pp
1.16 jmc 73: The manual includes both tutorial and reference sections:
74: .Bl -ohang
75: .It Sy Some Simple Examples
76: .It Sy Format of the Input File
77: .It Sy Patterns
78: The extended regular expressions used by
79: .Nm .
80: .It Sy How the Input is Matched
81: The rules for determining what has been matched.
82: .It Sy Actions
83: How to specify what to do when a pattern is matched.
84: .It Sy The Generated Scanner
85: Details regarding the scanner that
86: .Nm
87: produces;
88: how to control the input source.
89: .It Sy Start Conditions
90: Introducing context into scanners, and managing
91: .Qq mini-scanners .
92: .It Sy Multiple Input Buffers
93: How to manipulate multiple input sources;
94: how to scan from strings instead of files.
95: .It Sy End-of-File Rules
96: Special rules for matching the end of the input.
97: .It Sy Miscellaneous Macros
98: A summary of macros available to the actions.
99: .It Sy Values Available to the User
100: A summary of values available to the actions.
101: .It Sy Interfacing with Yacc
102: Connecting flex scanners together with
103: .Xr yacc 1
104: parsers.
105: .It Sy Options
106: .Nm
107: command-line options, and the
108: .Dq %option
109: directive.
110: .It Sy Performance Considerations
111: How to make scanners go as fast as possible.
112: .It Sy Generating C++ Scanners
113: The
114: .Pq experimental
115: facility for generating C++ scanner classes.
116: .It Sy Incompatibilities with Lex and POSIX
117: How
118: .Nm
1.36 schwarze 119: differs from
120: .At
121: .Nm lex
122: and the
1.16 jmc 123: .Tn POSIX
1.36 schwarze 124: .Nm lex
125: standard.
1.16 jmc 126: .It Sy Files
127: Files used by
128: .Nm .
129: .It Sy Diagnostics
130: Those error messages produced by
131: .Nm
132: .Pq or scanners it generates
133: whose meanings might not be apparent.
134: .It Sy See Also
135: Other documentation, related tools.
136: .It Sy Authors
137: Includes contact information.
138: .It Sy Bugs
139: Known problems with
140: .Nm .
141: .El
142: .Sh SOME SIMPLE EXAMPLES
1.1 deraadt 143: First some simple examples to get the flavor of how one uses
1.16 jmc 144: .Nm .
1.1 deraadt 145: The following
1.16 jmc 146: .Nm
1.1 deraadt 147: input specifies a scanner which whenever it encounters the string
1.16 jmc 148: .Qq username
149: will replace it with the user's login name:
150: .Bd -literal -offset indent
151: %%
152: username printf("%s", getlogin());
153: .Ed
154: .Pp
1.1 deraadt 155: By default, any text not matched by a
1.16 jmc 156: .Nm
157: scanner is copied to the output, so the net effect of this scanner is
158: to copy its input file to its output with each occurrence of
159: .Qq username
160: expanded.
161: In this input, there is just one rule.
162: .Qq username
163: is the
164: .Em pattern
165: and the
166: .Qq printf
167: is the
168: .Em action .
169: The
170: .Qq %%
171: marks the beginning of the rules.
172: .Pp
1.1 deraadt 173: Here's another simple example:
1.16 jmc 174: .Bd -literal -offset indent
1.20 pvalchev 175: %{
1.16 jmc 176: int num_lines = 0, num_chars = 0;
1.20 pvalchev 177: %}
1.1 deraadt 178:
1.16 jmc 179: %%
180: \en ++num_lines; ++num_chars;
181: \&. ++num_chars;
182:
183: %%
184: main()
185: {
186: yylex();
187: printf("# of lines = %d, # of chars = %d\en",
188: num_lines, num_chars);
189: }
190: .Ed
191: .Pp
1.1 deraadt 192: This scanner counts the number of characters and the number
1.16 jmc 193: of lines in its input
194: (it produces no output other than the final report on the counts).
195: The first line declares two globals,
196: .Qq num_lines
197: and
198: .Qq num_chars ,
199: which are accessible both inside
200: .Fn yylex
1.1 deraadt 201: and in the
1.16 jmc 202: .Fn main
203: routine declared after the second
204: .Qq %% .
205: There are two rules, one which matches a newline
206: .Pq \&"\en\&"
207: and increments both the line count and the character count,
208: and one which matches any character other than a newline
209: (indicated by the
210: .Qq \&.
211: regular expression).
212: .Pp
1.1 deraadt 213: A somewhat more complicated example:
1.16 jmc 214: .Bd -literal -offset indent
215: /* scanner for a toy Pascal-like language */
1.1 deraadt 216:
1.16 jmc 217: %{
218: /* need this for the call to atof() below */
219: #include <math.h>
220: %}
1.1 deraadt 221:
1.16 jmc 222: DIGIT [0-9]
223: ID [a-z][a-z0-9]*
1.1 deraadt 224:
1.16 jmc 225: %%
1.1 deraadt 226:
1.16 jmc 227: {DIGIT}+ {
228: printf("An integer: %s (%d)\en", yytext,
229: atoi(yytext));
230: }
1.1 deraadt 231:
1.16 jmc 232: {DIGIT}+"."{DIGIT}* {
233: printf("A float: %s (%g)\en", yytext,
234: atof(yytext));
235: }
1.1 deraadt 236:
1.16 jmc 237: if|then|begin|end|procedure|function {
238: printf("A keyword: %s\en", yytext);
239: }
1.1 deraadt 240:
1.16 jmc 241: {ID} printf("An identifier: %s\en", yytext);
1.1 deraadt 242:
1.16 jmc 243: "+"|"-"|"*"|"/" printf("An operator: %s\en", yytext);
1.1 deraadt 244:
1.16 jmc 245: "{"[^}\en]*"}" /* eat up one-line comments */
1.1 deraadt 246:
1.16 jmc 247: [ \et\en]+ /* eat up whitespace */
1.1 deraadt 248:
1.16 jmc 249: \&. printf("Unrecognized character: %s\en", yytext);
1.1 deraadt 250:
1.16 jmc 251: %%
1.1 deraadt 252:
1.16 jmc 253: main(int argc, char *argv[])
254: {
255: ++argv; --argc; /* skip over program name */
256: if (argc > 0)
257: yyin = fopen(argv[0], "r");
1.1 deraadt 258: else
259: yyin = stdin;
1.7 aaron 260:
1.1 deraadt 261: yylex();
1.16 jmc 262: }
263: .Ed
264: .Pp
265: This is the beginnings of a simple scanner for a language like Pascal.
266: It identifies different types of
267: .Em tokens
1.1 deraadt 268: and reports on what it has seen.
1.16 jmc 269: .Pp
270: The details of this example will be explained in the following sections.
271: .Sh FORMAT OF THE INPUT FILE
1.1 deraadt 272: The
1.16 jmc 273: .Nm
1.1 deraadt 274: input file consists of three sections, separated by a line with just
1.16 jmc 275: .Qq %%
1.1 deraadt 276: in it:
1.16 jmc 277: .Bd -unfilled -offset indent
278: definitions
279: %%
280: rules
281: %%
282: user code
283: .Ed
284: .Pp
1.1 deraadt 285: The
1.16 jmc 286: .Em definitions
1.1 deraadt 287: section contains declarations of simple
1.16 jmc 288: .Em name
1.1 deraadt 289: definitions to simplify the scanner specification, and declarations of
1.16 jmc 290: .Em start conditions ,
1.1 deraadt 291: which are explained in a later section.
1.16 jmc 292: .Pp
1.1 deraadt 293: Name definitions have the form:
1.16 jmc 294: .Pp
295: .D1 name definition
296: .Pp
297: The
298: .Qq name
299: is a word beginning with a letter or an underscore
300: .Pq Sq _
301: followed by zero or more letters, digits,
302: .Sq _ ,
303: or
304: .Sq -
305: .Pq dash .
1.8 aaron 306: The definition is taken to begin at the first non-whitespace character
1.1 deraadt 307: following the name and continuing to the end of the line.
1.16 jmc 308: The definition can subsequently be referred to using
309: .Qq {name} ,
310: which will expand to
311: .Qq (definition) .
312: For example:
313: .Bd -literal -offset indent
314: DIGIT [0-9]
315: ID [a-z][a-z0-9]*
316: .Ed
317: .Pp
318: This defines
319: .Qq DIGIT
320: to be a regular expression which matches a single digit, and
321: .Qq ID
322: to be a regular expression which matches a letter
1.1 deraadt 323: followed by zero-or-more letters-or-digits.
324: A subsequent reference to
1.16 jmc 325: .Pp
326: .Dl {DIGIT}+"."{DIGIT}*
327: .Pp
1.1 deraadt 328: is identical to
1.16 jmc 329: .Pp
330: .Dl ([0-9])+"."([0-9])*
331: .Pp
332: and matches one-or-more digits followed by a
333: .Sq .\&
334: followed by zero-or-more digits.
335: .Pp
1.1 deraadt 336: The
1.16 jmc 337: .Em rules
1.1 deraadt 338: section of the
1.16 jmc 339: .Nm
1.1 deraadt 340: input contains a series of rules of the form:
1.16 jmc 341: .Pp
1.35 schwarze 342: .Dl pattern action
1.16 jmc 343: .Pp
344: The pattern must be unindented and the action must begin
1.1 deraadt 345: on the same line.
1.16 jmc 346: .Pp
1.1 deraadt 347: See below for a further description of patterns and actions.
1.16 jmc 348: .Pp
1.1 deraadt 349: Finally, the user code section is simply copied to
1.16 jmc 350: .Pa lex.yy.c
1.1 deraadt 351: verbatim.
1.16 jmc 352: It is used for companion routines which call or are called by the scanner.
353: The presence of this section is optional;
1.1 deraadt 354: if it is missing, the second
1.16 jmc 355: .Qq %%
356: in the input file may be skipped too.
357: .Pp
358: In the definitions and rules sections, any indented text or text enclosed in
359: .Sq %{
1.1 deraadt 360: and
1.16 jmc 361: .Sq %}
362: is copied verbatim to the output
363: .Pq with the %{}'s removed .
1.1 deraadt 364: The %{}'s must appear unindented on lines by themselves.
1.16 jmc 365: .Pp
1.1 deraadt 366: In the rules section,
1.16 jmc 367: any indented or %{} text appearing before the first rule may be used to
368: declare variables which are local to the scanning routine and
369: .Pq after the declarations
1.1 deraadt 370: code which is to be executed whenever the scanning routine is entered.
371: Other indented or %{} text in the rule section is still copied to the output,
372: but its meaning is not well-defined and it may well cause compile-time
373: errors (this feature is present for
1.16 jmc 374: .Tn POSIX
1.1 deraadt 375: compliance; see below for other such features).
1.16 jmc 376: .Pp
377: In the definitions section
378: .Pq but not in the rules section ,
379: an unindented comment
380: (i.e., a line beginning with
381: .Qq /* )
382: is also copied verbatim to the output up to the next
383: .Qq */ .
384: .Sh PATTERNS
1.1 deraadt 385: The patterns in the input are written using an extended set of regular
1.16 jmc 386: expressions.
387: These are:
388: .Bl -tag -width "XXXXXXXX"
389: .It x
390: Match the character
391: .Sq x .
392: .It .\&
393: Any character
394: .Pq byte
395: except newline.
396: .It [xyz]
397: A
398: .Qq character class ;
399: in this case, the pattern matches either an
400: .Sq x ,
401: a
402: .Sq y ,
403: or a
404: .Sq z .
405: .It [abj-oZ]
406: A
407: .Qq character class
408: with a range in it; matches an
409: .Sq a ,
410: a
411: .Sq b ,
412: any letter from
413: .Sq j
414: through
415: .Sq o ,
416: or a
417: .Sq Z .
418: .It [^A-Z]
419: A
420: .Qq negated character class ,
421: i.e., any character but those in the class.
422: In this case, any character EXCEPT an uppercase letter.
423: .It [^A-Z\en]
424: Any character EXCEPT an uppercase letter or a newline.
425: .It r*
426: Zero or more r's, where
427: .Sq r
428: is any regular expression.
429: .It r+
430: One or more r's.
431: .It r?
432: Zero or one r's (that is,
433: .Qq an optional r ) .
434: .It r{2,5}
435: Anywhere from two to five r's.
436: .It r{2,}
437: Two or more r's.
438: .It r{4}
439: Exactly 4 r's.
440: .It {name}
441: The expansion of the
442: .Qq name
443: definition
444: .Pq see above .
445: .It \&"[xyz]\e\&"foo\&"
446: The literal string: [xyz]"foo.
447: .It \eX
448: If
449: .Sq X
450: is an
451: .Sq a ,
452: .Sq b ,
453: .Sq f ,
454: .Sq n ,
455: .Sq r ,
456: .Sq t ,
457: or
458: .Sq v ,
459: then the ANSI-C interpretation of
460: .Sq \eX .
461: Otherwise, a literal
462: .Sq X
463: (used to escape operators such as
464: .Sq * ) .
465: .It \e0
466: A NUL character
467: .Pq ASCII code 0 .
468: .It \e123
469: The character with octal value 123.
470: .It \ex2a
471: The character with hexadecimal value 2a.
472: .It (r)
473: Match an
474: .Sq r ;
475: parentheses are used to override precedence
476: .Pq see below .
477: .It rs
478: The regular expression
479: .Sq r
480: followed by the regular expression
481: .Sq s ;
482: called
483: .Qq concatenation .
484: .It r|s
485: Either an
486: .Sq r
487: or an
488: .Sq s .
489: .It r/s
490: An
491: .Sq r ,
492: but only if it is followed by an
493: .Sq s .
494: The text matched by
495: .Sq s
496: is included when determining whether this rule is the
497: .Qq longest match ,
498: but is then returned to the input before the action is executed.
499: So the action only sees the text matched by
500: .Sq r .
501: This type of pattern is called
502: .Qq trailing context .
503: (There are some combinations of r/s that
504: .Nm
505: cannot match correctly; see notes in the
506: .Sx BUGS
507: section below regarding
508: .Qq dangerous trailing context . )
509: .It ^r
510: An
511: .Sq r ,
512: but only at the beginning of a line
513: (i.e., just starting to scan, or right after a newline has been scanned).
514: .It r$
515: An
516: .Sq r ,
517: but only at the end of a line
518: .Pq i.e., just before a newline .
519: Equivalent to
520: .Qq r/\en .
521: .Pp
522: Note that
523: .Nm flex Ns 's
524: notion of
525: .Qq newline
526: is exactly whatever the C compiler used to compile
527: .Nm
528: interprets
529: .Sq \en
530: as.
531: .\" In particular, on some DOS systems you must either filter out \er's in the
532: .\" input yourself, or explicitly use r/\er\en for
533: .\" .Qq r$ .
534: .It <s>r
535: An
536: .Sq r ,
537: but only in start condition
538: .Sq s
539: .Pq see below for discussion of start conditions .
540: .It <s1,s2,s3>r
541: The same, but in any of start conditions s1, s2, or s3.
542: .It <*>r
543: An
544: .Sq r
545: in any start condition, even an exclusive one.
546: .It <<EOF>>
547: An end-of-file.
548: .It <s1,s2><<EOF>>
549: An end-of-file when in start condition s1 or s2.
550: .El
551: .Pp
1.1 deraadt 552: Note that inside of a character class, all regular expression operators
1.16 jmc 553: lose their special meaning except escape
554: .Pq Sq \e
555: and the character class operators,
556: .Sq - ,
557: .Sq ]\& ,
558: and, at the beginning of the class,
559: .Sq ^ .
560: .Pp
1.1 deraadt 561: The regular expressions listed above are grouped according to
562: precedence, from highest precedence at the top to lowest at the bottom.
1.16 jmc 563: Those grouped together have equal precedence.
564: For example,
565: .Pp
566: .D1 foo|bar*
567: .Pp
1.1 deraadt 568: is the same as
1.16 jmc 569: .Pp
570: .D1 (foo)|(ba(r*))
571: .Pp
572: since the
573: .Sq *
574: operator has higher precedence than concatenation,
575: and concatenation higher than alternation
576: .Pq Sq |\& .
577: This pattern therefore matches
578: .Em either
579: the string
580: .Qq foo
581: .Em or
582: the string
583: .Qq ba
584: followed by zero-or-more r's.
585: To match
586: .Qq foo
587: or zero-or-more "bar"'s,
588: use:
589: .Pp
590: .D1 foo|(bar)*
591: .Pp
1.1 deraadt 592: and to match zero-or-more "foo"'s-or-"bar"'s:
1.16 jmc 593: .Pp
594: .D1 (foo|bar)*
595: .Pp
1.1 deraadt 596: In addition to characters and ranges of characters, character classes
597: can also contain character class
1.16 jmc 598: .Em expressions .
1.1 deraadt 599: These are expressions enclosed inside
1.16 jmc 600: .Sq [:
601: and
602: .Sq :]
603: delimiters (which themselves must appear between the
1.26 schwarze 604: .Sq \&[
1.1 deraadt 605: and
1.16 jmc 606: .Sq ]\&
607: of the
1.1 deraadt 608: character class; other elements may occur inside the character class, too).
609: The valid expressions are:
1.16 jmc 610: .Bd -unfilled -offset indent
611: [:alnum:] [:alpha:] [:blank:]
612: [:cntrl:] [:digit:] [:graph:]
613: [:lower:] [:print:] [:punct:]
614: [:space:] [:upper:] [:xdigit:]
615: .Ed
616: .Pp
1.1 deraadt 617: These expressions all designate a set of characters equivalent to
618: the corresponding standard C
1.16 jmc 619: .Fn isXXX
620: function.
621: For example, [:alnum:] designates those characters for which
622: .Xr isalnum 3
623: returns true \- i.e., any alphabetic or numeric.
1.1 deraadt 624: Some systems don't provide
1.16 jmc 625: .Xr isblank 3 ,
626: so
627: .Nm
628: defines [:blank:] as a blank or a tab.
629: .Pp
1.1 deraadt 630: For example, the following character classes are all equivalent:
1.16 jmc 631: .Bd -unfilled -offset indent
632: [[:alnum:]]
633: [[:alpha:][:digit:]]
634: [[:alpha:]0-9]
635: [a-zA-Z0-9]
636: .Ed
637: .Pp
638: If the scanner is case-insensitive (the
639: .Fl i
640: flag), then [:upper:] and [:lower:] are equivalent to [:alpha:].
641: .Pp
1.1 deraadt 642: Some notes on patterns:
1.16 jmc 643: .Bl -dash
644: .It
645: A negated character class such as the example
646: .Qq [^A-Z]
647: above will match a newline unless "\en"
648: .Pq or an equivalent escape sequence
649: is one of the characters explicitly present in the negated character class
650: (e.g.,
651: .Qq [^A-Z\en] ) .
652: This is unlike how many other regular expression tools treat negated character
653: classes, but unfortunately the inconsistency is historically entrenched.
654: Matching newlines means that a pattern like
655: .Qq [^"]*
656: can match the entire input unless there's another quote in the input.
657: .It
658: A rule can have at most one instance of trailing context
659: (the
660: .Sq /
661: operator or the
662: .Sq $
663: operator).
664: The start condition,
665: .Sq ^ ,
666: and
667: .Qq <<EOF>>
668: patterns can only occur at the beginning of a pattern, and, as well as with
669: .Sq /
670: and
671: .Sq $ ,
672: cannot be grouped inside parentheses.
673: A
674: .Sq ^
675: which does not occur at the beginning of a rule or a
676: .Sq $
677: which does not occur at the end of a rule loses its special properties
678: and is treated as a normal character.
679: .It
1.1 deraadt 680: The following are illegal:
1.16 jmc 681: .Bd -unfilled -offset indent
682: foo/bar$
683: <sc1>foo<sc2>bar
684: .Ed
685: .Pp
686: Note that the first of these, can be written
687: .Qq foo/bar\en .
688: .It
689: The following will result in
690: .Sq $
691: or
692: .Sq ^
693: being treated as a normal character:
694: .Bd -unfilled -offset indent
695: foo|(bar$)
696: foo|^bar
697: .Ed
698: .Pp
699: If what's wanted is a
700: .Qq foo
701: or a bar-followed-by-a-newline, the following could be used
702: (the special
703: .Sq |\&
704: action is explained below):
705: .Bd -unfilled -offset indent
706: foo |
707: bar$ /* action goes here */
708: .Ed
709: .Pp
1.1 deraadt 710: A similar trick will work for matching a foo or a
711: bar-at-the-beginning-of-a-line.
1.16 jmc 712: .El
713: .Sh HOW THE INPUT IS MATCHED
714: When the generated scanner is run,
715: it analyzes its input looking for strings which match any of its patterns.
716: If it finds more than one match,
717: it takes the one matching the most text
718: (for trailing context rules, this includes the length of the trailing part,
719: even though it will then be returned to the input).
720: If it finds two or more matches of the same length,
721: the rule listed first in the
722: .Nm
1.1 deraadt 723: input file is chosen.
1.16 jmc 724: .Pp
1.1 deraadt 725: Once the match is determined, the text corresponding to the match
726: (called the
1.16 jmc 727: .Em token )
1.1 deraadt 728: is made available in the global character pointer
1.16 jmc 729: .Fa yytext ,
1.1 deraadt 730: and its length in the global integer
1.16 jmc 731: .Fa yyleng .
1.1 deraadt 732: The
1.16 jmc 733: .Em action
734: corresponding to the matched pattern is then executed
735: .Pq a more detailed description of actions follows ,
736: and then the remaining input is scanned for another match.
737: .Pp
738: If no match is found, then the default rule is executed:
739: the next character in the input is considered matched and
740: copied to the standard output.
741: Thus, the simplest legal
742: .Nm
1.1 deraadt 743: input is:
1.16 jmc 744: .Pp
745: .D1 %%
746: .Pp
747: which generates a scanner that simply copies its input
748: .Pq one character at a time
749: to its output.
750: .Pp
1.1 deraadt 751: Note that
1.16 jmc 752: .Fa yytext
753: can be defined in two different ways:
754: either as a character pointer or as a character array.
755: Which definition
756: .Nm
757: uses can be controlled by including one of the special directives
758: .Dq %pointer
759: or
760: .Dq %array
761: in the first
762: .Pq definitions
763: section of flex input.
764: The default is
765: .Dq %pointer ,
766: unless the
767: .Fl l
1.36 schwarze 768: .Nm lex
769: compatibility option is used, in which case
1.16 jmc 770: .Fa yytext
1.1 deraadt 771: will be an array.
772: The advantage of using
1.16 jmc 773: .Dq %pointer
1.1 deraadt 774: is substantially faster scanning and no buffer overflow when matching
1.16 jmc 775: very large tokens
776: .Pq unless not enough dynamic memory is available .
777: The disadvantage is that actions are restricted in how they can modify
778: .Fa yytext
779: .Pq see the next section ,
780: and calls to the
781: .Fn unput
1.10 deraadt 782: function destroy the present contents of
1.16 jmc 783: .Fa yytext ,
1.1 deraadt 784: which can be a considerable porting headache when moving between different
1.16 jmc 785: .Nm lex
1.1 deraadt 786: versions.
1.16 jmc 787: .Pp
1.1 deraadt 788: The advantage of
1.16 jmc 789: .Dq %array
790: is that
791: .Fa yytext
792: can be modified as much as wanted, and calls to
793: .Fn unput
1.1 deraadt 794: do not destroy
1.16 jmc 795: .Fa yytext
796: .Pq see below .
797: Furthermore, existing
798: .Nm lex
1.1 deraadt 799: programs sometimes access
1.16 jmc 800: .Fa yytext
1.1 deraadt 801: externally using declarations of the form:
1.16 jmc 802: .Pp
803: .D1 extern char yytext[];
804: .Pp
1.1 deraadt 805: This definition is erroneous when used with
1.16 jmc 806: .Dq %pointer ,
1.1 deraadt 807: but correct for
1.16 jmc 808: .Dq %array .
809: .Pp
810: .Dq %array
1.1 deraadt 811: defines
1.16 jmc 812: .Fa yytext
1.1 deraadt 813: to be an array of
1.16 jmc 814: .Dv YYLMAX
815: characters, which defaults to a fairly large value.
816: The size can be changed by simply #define'ing
817: .Dv YYLMAX
818: to a different value in the first section of
819: .Nm
820: input.
821: As mentioned above, with
822: .Dq %pointer
823: yytext grows dynamically to accommodate large tokens.
824: While this means a
825: .Dq %pointer
826: scanner can accommodate very large tokens
827: .Pq such as matching entire blocks of comments ,
828: bear in mind that each time the scanner must resize
829: .Fa yytext
1.1 deraadt 830: it also must rescan the entire token from the beginning, so matching such
831: tokens can prove slow.
1.16 jmc 832: .Fa yytext
833: presently does not dynamically grow if a call to
834: .Fn unput
1.1 deraadt 835: results in too much text being pushed back; instead, a run-time error results.
1.16 jmc 836: .Pp
837: Also note that
838: .Dq %array
839: cannot be used with C++ scanner classes
840: .Pq the c++ option; see below .
841: .Sh ACTIONS
842: Each pattern in a rule has a corresponding action,
843: which can be any arbitrary C statement.
844: The pattern ends at the first non-escaped whitespace character;
845: the remainder of the line is its action.
846: If the action is empty,
847: then when the pattern is matched the input token is simply discarded.
848: For example, here is the specification for a program
849: which deletes all occurrences of
850: .Qq zap me
851: from its input:
852: .Bd -literal -offset indent
853: %%
854: "zap me"
855: .Ed
856: .Pp
1.1 deraadt 857: (It will copy all other characters in the input to the output since
858: they will be matched by the default rule.)
1.16 jmc 859: .Pp
1.1 deraadt 860: Here is a program which compresses multiple blanks and tabs down to
861: a single blank, and throws away whitespace found at the end of a line:
1.16 jmc 862: .Bd -literal -offset indent
863: %%
864: [ \et]+ putchar(' ');
865: [ \et]+$ /* ignore this token */
866: .Ed
867: .Pp
868: If the action contains a
869: .Sq { ,
870: then the action spans till the balancing
871: .Sq }
1.1 deraadt 872: is found, and the action may cross multiple lines.
1.16 jmc 873: .Nm
1.1 deraadt 874: knows about C strings and comments and won't be fooled by braces found
875: within them, but also allows actions to begin with
1.16 jmc 876: .Sq %{
1.1 deraadt 877: and will consider the action to be all the text up to the next
1.16 jmc 878: .Sq %}
879: .Pq regardless of ordinary braces inside the action .
880: .Pp
881: An action consisting solely of a vertical bar
882: .Pq Sq |\&
883: means
884: .Qq same as the action for the next rule .
885: See below for an illustration.
886: .Pp
887: Actions can include arbitrary C code,
888: including return statements to return a value to whatever routine called
889: .Fn yylex .
1.1 deraadt 890: Each time
1.16 jmc 891: .Fn yylex
892: is called, it continues processing tokens from where it last left off
893: until it either reaches the end of the file or executes a return.
894: .Pp
1.1 deraadt 895: Actions are free to modify
1.16 jmc 896: .Fa yytext
897: except for lengthening it
898: (adding characters to its end \- these will overwrite later characters in the
899: input stream).
900: This, however, does not apply when using
901: .Dq %array
902: .Pq see above ;
903: in that case,
904: .Fa yytext
1.1 deraadt 905: may be freely modified in any way.
1.16 jmc 906: .Pp
1.1 deraadt 907: Actions are free to modify
1.16 jmc 908: .Fa yyleng
1.1 deraadt 909: except they should not do so if the action also includes use of
1.16 jmc 910: .Fn yymore
911: .Pq see below .
912: .Pp
1.1 deraadt 913: There are a number of special directives which can be included within
914: an action:
1.16 jmc 915: .Bl -tag -width Ds
916: .It ECHO
917: Copies
918: .Fa yytext
919: to the scanner's output.
920: .It BEGIN
921: Followed by the name of a start condition, places the scanner in the
922: corresponding start condition
923: .Pq see below .
924: .It REJECT
925: Directs the scanner to proceed on to the
926: .Qq second best
927: rule which matched the input
928: .Pq or a prefix of the input .
929: The rule is chosen as described above in
930: .Sx HOW THE INPUT IS MATCHED ,
931: and
932: .Fa yytext
1.1 deraadt 933: and
1.16 jmc 934: .Fa yyleng
1.1 deraadt 935: set up appropriately.
936: It may either be one which matched as much text
937: as the originally chosen rule but came later in the
1.16 jmc 938: .Nm
1.1 deraadt 939: input file, or one which matched less text.
940: For example, the following will both count the
1.16 jmc 941: words in the input and call the routine
942: .Fn special
943: whenever
944: .Qq frob
945: is seen:
946: .Bd -literal -offset indent
947: int word_count = 0;
948: %%
949:
950: frob special(); REJECT;
951: [^ \et\en]+ ++word_count;
952: .Ed
953: .Pp
1.1 deraadt 954: Without the
1.16 jmc 955: .Em REJECT ,
956: any "frob"'s in the input would not be counted as words,
957: since the scanner normally executes only one action per token.
1.1 deraadt 958: Multiple
1.16 jmc 959: .Em REJECT Ns 's
960: are allowed,
961: each one finding the next best choice to the currently active rule.
962: For example, when the following scanner scans the token
963: .Qq abcd ,
964: it will write
965: .Qq abcdabcaba
966: to the output:
967: .Bd -literal -offset indent
968: %%
969: a |
970: ab |
971: abc |
972: abcd ECHO; REJECT;
973: \&.|\en /* eat up any unmatched character */
974: .Ed
975: .Pp
1.1 deraadt 976: (The first three rules share the fourth's action since they use
1.16 jmc 977: the special
978: .Sq |\&
979: action.)
980: .Em REJECT
1.1 deraadt 981: is a particularly expensive feature in terms of scanner performance;
1.16 jmc 982: if it is used in any of the scanner's actions it will slow down
983: all of the scanner's matching.
984: Furthermore,
985: .Em REJECT
1.1 deraadt 986: cannot be used with the
1.16 jmc 987: .Fl Cf
1.1 deraadt 988: or
1.16 jmc 989: .Fl CF
990: options
991: .Pq see below .
992: .Pp
1.1 deraadt 993: Note also that unlike the other special actions,
1.16 jmc 994: .Em REJECT
1.1 deraadt 995: is a
1.16 jmc 996: .Em branch ;
997: code immediately following it in the action will not be executed.
998: .It yymore()
999: Tells the scanner that the next time it matches a rule, the corresponding
1000: token should be appended onto the current value of
1001: .Fa yytext
1002: rather than replacing it.
1003: For example, given the input
1004: .Qq mega-kludge
1005: the following will write
1006: .Qq mega-mega-kludge
1007: to the output:
1008: .Bd -literal -offset indent
1009: %%
1010: mega- ECHO; yymore();
1011: kludge ECHO;
1012: .Ed
1013: .Pp
1014: First
1015: .Qq mega-
1016: is matched and echoed to the output.
1017: Then
1018: .Qq kludge
1019: is matched, but the previous
1020: .Qq mega-
1021: is still hanging around at the beginning of
1022: .Fa yytext
1.1 deraadt 1023: so the
1.16 jmc 1024: .Em ECHO
1025: for the
1026: .Qq kludge
1027: rule will actually write
1028: .Qq mega-kludge .
1029: .Pp
1.1 deraadt 1030: Two notes regarding use of
1.16 jmc 1031: .Fn yymore :
1.1 deraadt 1032: First,
1.16 jmc 1033: .Fn yymore
1.1 deraadt 1034: depends on the value of
1.16 jmc 1035: .Fa yyleng
1036: correctly reflecting the size of the current token, so
1037: .Fa yyleng
1038: must not be modified when using
1039: .Fn yymore .
1.1 deraadt 1040: Second, the presence of
1.16 jmc 1041: .Fn yymore
1.1 deraadt 1042: in the scanner's action entails a minor performance penalty in the
1043: scanner's matching speed.
1.16 jmc 1044: .It yyless(n)
1045: Returns all but the first
1046: .Ar n
1.1 deraadt 1047: characters of the current token back to the input stream, where they
1048: will be rescanned when the scanner looks for the next match.
1.16 jmc 1049: .Fa yytext
1.1 deraadt 1050: and
1.16 jmc 1051: .Fa yyleng
1.1 deraadt 1052: are adjusted appropriately (e.g.,
1.16 jmc 1053: .Fa yyleng
1.1 deraadt 1054: will now be equal to
1.16 jmc 1055: .Ar n ) .
1056: For example, on the input
1057: .Qq foobar
1058: the following will write out
1059: .Qq foobarbar :
1060: .Bd -literal -offset indent
1061: %%
1062: foobar ECHO; yyless(3);
1063: [a-z]+ ECHO;
1064: .Ed
1065: .Pp
1.1 deraadt 1066: An argument of 0 to
1.16 jmc 1067: .Fa yyless
1068: will cause the entire current input string to be scanned again.
1069: Unless how the scanner will subsequently process its input has been changed
1070: (using
1071: .Em BEGIN ,
1072: for example),
1073: this will result in an endless loop.
1074: .Pp
1.1 deraadt 1075: Note that
1.16 jmc 1076: .Fa yyless
1077: is a macro and can only be used in the
1078: .Nm
1079: input file, not from other source files.
1080: .It unput(c)
1081: Puts the character
1082: .Ar c
1083: back into the input stream.
1084: It will be the next character scanned.
1.1 deraadt 1085: The following action will take the current token and cause it
1086: to be rescanned enclosed in parentheses.
1.16 jmc 1087: .Bd -literal -offset indent
1088: {
1089: int i;
1090: char *yycopy;
1091:
1092: /* Copy yytext because unput() trashes yytext */
1093: if ((yycopy = strdup(yytext)) == NULL)
1094: err(1, NULL);
1095: unput(')');
1096: for (i = yyleng - 1; i >= 0; --i)
1097: unput(yycopy[i]);
1098: unput('(');
1099: free(yycopy);
1100: }
1101: .Ed
1102: .Pp
1.1 deraadt 1103: Note that since each
1.16 jmc 1104: .Fn unput
1105: puts the given character back at the beginning of the input stream,
1106: pushing back strings must be done back-to-front.
1107: .Pp
1.1 deraadt 1108: An important potential problem when using
1.16 jmc 1109: .Fn unput
1110: is that if using
1111: .Dq %pointer
1112: .Pq the default ,
1113: a call to
1114: .Fn unput
1115: destroys the contents of
1116: .Fa yytext ,
1.1 deraadt 1117: starting with its rightmost character and devouring one character to
1.16 jmc 1118: the left with each call.
1119: If the value of
1120: .Fa yytext
1121: should be preserved after a call to
1122: .Fn unput
1123: .Pq as in the above example ,
1124: it must either first be copied elsewhere, or the scanner must be built using
1125: .Dq %array
1126: instead (see
1127: .Sx HOW THE INPUT IS MATCHED ) .
1128: .Pp
1129: Finally, note that EOF cannot be put back
1.1 deraadt 1130: to attempt to mark the input stream with an end-of-file.
1.16 jmc 1131: .It input()
1132: Reads the next character from the input stream.
1133: For example, the following is one way to eat up C comments:
1134: .Bd -literal -offset indent
1135: %%
1136: "/*" {
1137: int c;
1138:
1139: for (;;) {
1140: while ((c = input()) != '*' && c != EOF)
1141: ; /* eat up text of comment */
1142:
1143: if (c == '*') {
1144: while ((c = input()) == '*')
1145: ;
1146: if (c == '/')
1147: break; /* found the end */
1148: }
1149:
1150: if (c == EOF) {
1151: errx(1, "EOF in comment");
1.1 deraadt 1152: break;
1153: }
1.16 jmc 1154: }
1155: }
1156: .Ed
1157: .Pp
1158: (Note that if the scanner is compiled using C++, then
1159: .Fn input
1.1 deraadt 1160: is instead referred to as
1.16 jmc 1161: .Fn yyinput ,
1162: in order to avoid a name clash with the C++ stream by the name of input.)
1163: .It YY_FLUSH_BUFFER
1164: Flushes the scanner's internal buffer
1165: so that the next time the scanner attempts to match a token,
1166: it will first refill the buffer using
1167: .Dv YY_INPUT
1168: (see
1169: .Sx THE GENERATED SCANNER ,
1170: below).
1171: This action is a special case of the more general
1172: .Fn yy_flush_buffer
1173: function, described below in the section
1174: .Sx MULTIPLE INPUT BUFFERS .
1175: .It yyterminate()
1176: Can be used in lieu of a return statement in an action.
1177: It terminates the scanner and returns a 0 to the scanner's caller, indicating
1178: .Qq all done .
1.1 deraadt 1179: By default,
1.16 jmc 1180: .Fn yyterminate
1181: is also called when an end-of-file is encountered.
1182: It is a macro and may be redefined.
1183: .El
1184: .Sh THE GENERATED SCANNER
1.1 deraadt 1185: The output of
1.16 jmc 1186: .Nm
1.1 deraadt 1187: is the file
1.16 jmc 1188: .Pa lex.yy.c ,
1.1 deraadt 1189: which contains the scanning routine
1.16 jmc 1190: .Fn yylex ,
1191: a number of tables used by it for matching tokens,
1192: and a number of auxiliary routines and macros.
1193: By default,
1194: .Fn yylex
1.1 deraadt 1195: is declared as follows:
1.16 jmc 1196: .Bd -unfilled -offset indent
1197: int yylex()
1198: {
1199: ... various definitions and the actions in here ...
1200: }
1201: .Ed
1202: .Pp
1203: (If the environment supports function prototypes, then it will
1204: be "int yylex(void)".)
1205: This definition may be changed by defining the
1206: .Dv YY_DECL
1207: macro.
1208: For example:
1209: .Bd -literal -offset indent
1210: #define YY_DECL float lexscan(a, b) float a, b;
1211: .Ed
1212: .Pp
1213: would give the scanning routine the name
1214: .Em lexscan ,
1215: returning a float, and taking two floats as arguments.
1216: Note that if arguments are given to the scanning routine using a
1217: K&R-style/non-prototyped function declaration,
1218: the definition must be terminated with a semi-colon
1219: .Pq Sq ;\& .
1220: .Pp
1.1 deraadt 1221: Whenever
1.16 jmc 1222: .Fn yylex
1.1 deraadt 1223: is called, it scans tokens from the global input file
1.16 jmc 1224: .Pa yyin
1225: .Pq which defaults to stdin .
1226: It continues until it either reaches an end-of-file
1227: .Pq at which point it returns the value 0
1228: or one of its actions executes a
1229: .Em return
1.1 deraadt 1230: statement.
1.16 jmc 1231: .Pp
1.1 deraadt 1232: If the scanner reaches an end-of-file, subsequent calls are undefined
1233: unless either
1.16 jmc 1234: .Em yyin
1235: is pointed at a new input file
1236: .Pq in which case scanning continues from that file ,
1237: or
1238: .Fn yyrestart
1.1 deraadt 1239: is called.
1.16 jmc 1240: .Fn yyrestart
1.1 deraadt 1241: takes one argument, a
1.16 jmc 1242: .Fa FILE *
1243: pointer (which can be nil, if
1244: .Dv YY_INPUT
1245: has been set up to scan from a source other than
1246: .Em yyin ) ,
1.1 deraadt 1247: and initializes
1.16 jmc 1248: .Em yyin
1249: for scanning from that file.
1250: Essentially there is no difference between just assigning
1251: .Em yyin
1.1 deraadt 1252: to a new input file or using
1.16 jmc 1253: .Fn yyrestart
1254: to do so; the latter is available for compatibility with previous versions of
1255: .Nm ,
1.1 deraadt 1256: and because it can be used to switch input files in the middle of scanning.
1.16 jmc 1257: It can also be used to throw away the current input buffer,
1258: by calling it with an argument of
1259: .Em yyin ;
1.1 deraadt 1260: but better is to use
1.16 jmc 1261: .Dv YY_FLUSH_BUFFER
1262: .Pq see above .
1.1 deraadt 1263: Note that
1.16 jmc 1264: .Fn yyrestart
1265: does not reset the start condition to
1266: .Em INITIAL
1267: (see
1268: .Sx START CONDITIONS ,
1269: below).
1270: .Pp
1.1 deraadt 1271: If
1.16 jmc 1272: .Fn yylex
1.1 deraadt 1273: stops scanning due to executing a
1.16 jmc 1274: .Em return
1.1 deraadt 1275: statement in one of the actions, the scanner may then be called again and it
1276: will resume scanning where it left off.
1.16 jmc 1277: .Pp
1278: By default
1279: .Pq and for purposes of efficiency ,
1280: the scanner uses block-reads rather than simple
1281: .Xr getc 3
1.1 deraadt 1282: calls to read characters from
1.16 jmc 1283: .Em yyin .
1.1 deraadt 1284: The nature of how it gets its input can be controlled by defining the
1.16 jmc 1285: .Dv YY_INPUT
1.1 deraadt 1286: macro.
1.16 jmc 1287: .Dv YY_INPUT Ns 's
1288: calling sequence is
1289: .Qq YY_INPUT(buf,result,max_size) .
1290: Its action is to place up to
1291: .Dv max_size
1.1 deraadt 1292: characters in the character array
1.16 jmc 1293: .Em buf
1.1 deraadt 1294: and return in the integer variable
1.16 jmc 1295: .Em result
1296: either the number of characters read or the constant
1297: .Dv YY_NULL
1298: (0 on
1299: .Ux
1300: systems)
1301: to indicate
1302: .Dv EOF .
1303: The default
1304: .Dv YY_INPUT
1305: reads from the global file-pointer
1306: .Qq yyin .
1307: .Pp
1308: A sample definition of
1309: .Dv YY_INPUT
1310: .Pq in the definitions section of the input file :
1311: .Bd -unfilled -offset indent
1312: %{
1313: #define YY_INPUT(buf,result,max_size) \e
1314: { \e
1315: int c = getchar(); \e
1316: result = (c == EOF) ? YY_NULL : (buf[0] = c, 1); \e
1317: }
1318: %}
1319: .Ed
1320: .Pp
1.1 deraadt 1321: This definition will change the input processing to occur
1322: one character at a time.
1.16 jmc 1323: .Pp
1324: When the scanner receives an end-of-file indication from
1325: .Dv YY_INPUT ,
1.1 deraadt 1326: it then checks the
1.16 jmc 1327: .Fn yywrap
1328: function.
1329: If
1330: .Fn yywrap
1331: returns false
1332: .Pq zero ,
1333: then it is assumed that the function has gone ahead and set up
1334: .Em yyin
1335: to point to another input file, and scanning continues.
1336: If it returns true
1337: .Pq non-zero ,
1338: then the scanner terminates, returning 0 to its caller.
1339: Note that in either case, the start condition remains unchanged;
1340: it does not revert to
1341: .Em INITIAL .
1342: .Pp
1.1 deraadt 1343: If you do not supply your own version of
1.16 jmc 1344: .Fn yywrap ,
1.1 deraadt 1345: then you must either use
1.16 jmc 1346: .Dq %option noyywrap
1.1 deraadt 1347: (in which case the scanner behaves as though
1.16 jmc 1348: .Fn yywrap
1.1 deraadt 1349: returned 1), or you must link with
1.16 jmc 1350: .Fl lfl
1.1 deraadt 1351: to obtain the default version of the routine, which always returns 1.
1.16 jmc 1352: .Pp
1.1 deraadt 1353: Three routines are available for scanning from in-memory buffers rather
1354: than files:
1.16 jmc 1355: .Fn yy_scan_string ,
1356: .Fn yy_scan_bytes ,
1.1 deraadt 1357: and
1.16 jmc 1358: .Fn yy_scan_buffer .
1359: See the discussion of them below in the section
1360: .Sx MULTIPLE INPUT BUFFERS .
1361: .Pp
1.1 deraadt 1362: The scanner writes its
1.16 jmc 1363: .Em ECHO
1.1 deraadt 1364: output to the
1.16 jmc 1365: .Em yyout
1366: global
1367: .Pq default, stdout ,
1368: which may be redefined by the user simply by assigning it to some other
1369: .Va FILE
1.1 deraadt 1370: pointer.
1.16 jmc 1371: .Sh START CONDITIONS
1372: .Nm
1373: provides a mechanism for conditionally activating rules.
1374: Any rule whose pattern is prefixed with
1375: .Qq Aq sc
1376: will only be active when the scanner is in the start condition named
1377: .Qq sc .
1378: For example,
1379: .Bd -literal -offset indent
1380: <STRING>[^"]* { /* eat up the string body ... */
1381: ...
1382: }
1383: .Ed
1384: .Pp
1385: will be active only when the scanner is in the
1386: .Qq STRING
1387: start condition, and
1388: .Bd -literal -offset indent
1389: <INITIAL,STRING,QUOTE>\e. { /* handle an escape ... */
1390: ...
1391: }
1392: .Ed
1393: .Pp
1394: will be active only when the current start condition is either
1395: .Qq INITIAL ,
1396: .Qq STRING ,
1397: or
1398: .Qq QUOTE .
1399: .Pp
1400: Start conditions are declared in the definitions
1401: .Pq first
1402: section of the input using unindented lines beginning with either
1403: .Sq %s
1.1 deraadt 1404: or
1.16 jmc 1405: .Sq %x
1.1 deraadt 1406: followed by a list of names.
1407: The former declares
1.16 jmc 1408: .Em inclusive
1.1 deraadt 1409: start conditions, the latter
1.16 jmc 1410: .Em exclusive
1411: start conditions.
1412: A start condition is activated using the
1413: .Em BEGIN
1414: action.
1415: Until the next
1416: .Em BEGIN
1417: action is executed, rules with the given start condition will be active and
1.1 deraadt 1418: rules with other start conditions will be inactive.
1.16 jmc 1419: If the start condition is inclusive,
1.1 deraadt 1420: then rules with no start conditions at all will also be active.
1.16 jmc 1421: If it is exclusive,
1422: then only rules qualified with the start condition will be active.
1.1 deraadt 1423: A set of rules contingent on the same exclusive start condition
1424: describe a scanner which is independent of any of the other rules in the
1.16 jmc 1425: .Nm
1426: input.
1427: Because of this, exclusive start conditions make it easy to specify
1428: .Qq mini-scanners
1.1 deraadt 1429: which scan portions of the input that are syntactically different
1.16 jmc 1430: from the rest
1431: .Pq e.g., comments .
1432: .Pp
1.1 deraadt 1433: If the distinction between inclusive and exclusive start conditions
1434: is still a little vague, here's a simple example illustrating the
1.16 jmc 1435: connection between the two.
1436: The set of rules:
1437: .Bd -literal -offset indent
1438: %s example
1439: %%
1440:
1441: <example>foo do_something();
1442:
1443: bar something_else();
1444: .Ed
1445: .Pp
1.1 deraadt 1446: is equivalent to
1.16 jmc 1447: .Bd -literal -offset indent
1448: %x example
1449: %%
1450:
1451: <example>foo do_something();
1452:
1453: <INITIAL,example>bar something_else();
1454: .Ed
1455: .Pp
1.1 deraadt 1456: Without the
1.16 jmc 1457: .Aq INITIAL,example
1.1 deraadt 1458: qualifier, the
1.16 jmc 1459: .Dq bar
1460: pattern in the second example wouldn't be active
1461: .Pq i.e., couldn't match
1.1 deraadt 1462: when in start condition
1.16 jmc 1463: .Dq example .
1.1 deraadt 1464: If we just used
1.16 jmc 1465: .Aq example
1.1 deraadt 1466: to qualify
1.16 jmc 1467: .Dq bar ,
1.1 deraadt 1468: though, then it would only be active in
1.16 jmc 1469: .Dq example
1.1 deraadt 1470: and not in
1.16 jmc 1471: .Em INITIAL ,
1472: while in the first example it's active in both,
1473: because in the first example the
1474: .Dq example
1475: start condition is an inclusive
1476: .Pq Sq %s
1.1 deraadt 1477: start condition.
1.16 jmc 1478: .Pp
1.1 deraadt 1479: Also note that the special start-condition specifier
1.16 jmc 1480: .Sq Aq *
1481: matches every start condition.
1482: Thus, the above example could also have been written:
1483: .Bd -literal -offset indent
1484: %x example
1485: %%
1486:
1487: <example>foo do_something();
1488:
1489: <*>bar something_else();
1490: .Ed
1491: .Pp
1.1 deraadt 1492: The default rule (to
1.16 jmc 1493: .Em ECHO
1494: any unmatched character) remains active in start conditions.
1495: It is equivalent to:
1496: .Bd -literal -offset indent
1497: <*>.|\en ECHO;
1498: .Ed
1499: .Pp
1500: .Dq BEGIN(0)
1.1 deraadt 1501: returns to the original state where only the rules with
1.16 jmc 1502: no start conditions are active.
1503: This state can also be referred to as the start-condition
1504: .Em INITIAL ,
1505: so
1506: .Dq BEGIN(INITIAL)
1.1 deraadt 1507: is equivalent to
1.16 jmc 1508: .Dq BEGIN(0) .
1.1 deraadt 1509: (The parentheses around the start condition name are not required but
1510: are considered good style.)
1.16 jmc 1511: .Pp
1512: .Em BEGIN
1.1 deraadt 1513: actions can also be given as indented code at the beginning
1.16 jmc 1514: of the rules section.
1515: For example, the following will cause the scanner to enter the
1516: .Qq SPECIAL
1517: start condition whenever
1518: .Fn yylex
1.1 deraadt 1519: is called and the global variable
1.16 jmc 1520: .Fa enter_special
1.1 deraadt 1521: is true:
1.16 jmc 1522: .Bd -literal -offset indent
1523: int enter_special;
1.1 deraadt 1524:
1.16 jmc 1525: %x SPECIAL
1526: %%
1527: if (enter_special)
1.1 deraadt 1528: BEGIN(SPECIAL);
1529:
1.16 jmc 1530: <SPECIAL>blahblahblah
1531: \&...more rules follow...
1532: .Ed
1533: .Pp
1.1 deraadt 1534: To illustrate the uses of start conditions,
1535: here is a scanner which provides two different interpretations
1.16 jmc 1536: of a string like
1537: .Qq 123.456 .
1538: By default it will treat it as three tokens: the integer
1539: .Qq 123 ,
1540: a dot
1541: .Pq Sq .\& ,
1542: and the integer
1543: .Qq 456 .
1.1 deraadt 1544: But if the string is preceded earlier in the line by the string
1.16 jmc 1545: .Qq expect-floats
1546: it will treat it as a single token, the floating-point number 123.456:
1547: .Bd -literal -offset indent
1548: %{
1549: #include <math.h>
1550: %}
1551: %s expect
1552:
1553: %%
1554: expect-floats BEGIN(expect);
1555:
1556: <expect>[0-9]+"."[0-9]+ {
1557: printf("found a float, = %f\en",
1558: atof(yytext));
1559: }
1560: <expect>\en {
1561: /*
1562: * That's the end of the line, so
1563: * we need another "expect-number"
1564: * before we'll recognize any more
1565: * numbers.
1566: */
1567: BEGIN(INITIAL);
1568: }
1569:
1570: [0-9]+ {
1571: printf("found an integer, = %d\en",
1572: atoi(yytext));
1573: }
1574:
1575: "." printf("found a dot\en");
1576: .Ed
1577: .Pp
1578: Here is a scanner which recognizes
1579: .Pq and discards
1580: C comments while maintaining a count of the current input line:
1581: .Bd -literal -offset indent
1582: %x comment
1583: %%
1584: int line_num = 1;
1585:
1586: "/*" BEGIN(comment);
1587:
1588: <comment>[^*\en]* /* eat anything that's not a '*' */
1589: <comment>"*"+[^*/\en]* /* eat up '*'s not followed by '/'s */
1590: <comment>\en ++line_num;
1591: <comment>"*"+"/" BEGIN(INITIAL);
1592: .Ed
1593: .Pp
1.1 deraadt 1594: This scanner goes to a bit of trouble to match as much
1.16 jmc 1595: text as possible with each rule.
1596: In general, when attempting to write a high-speed scanner
1597: try to match as much as possible in each rule, as it's a big win.
1598: .Pp
1.10 deraadt 1599: Note that start-condition names are really integer values and
1.16 jmc 1600: can be stored as such.
1601: Thus, the above could be extended in the following fashion:
1602: .Bd -literal -offset indent
1603: %x comment foo
1604: %%
1605: int line_num = 1;
1606: int comment_caller;
1607:
1608: "/*" {
1609: comment_caller = INITIAL;
1610: BEGIN(comment);
1611: }
1612:
1613: \&...
1614:
1615: <foo>"/*" {
1616: comment_caller = foo;
1617: BEGIN(comment);
1618: }
1619:
1620: <comment>[^*\en]* /* eat anything that's not a '*' */
1621: <comment>"*"+[^*/\en]* /* eat up '*'s not followed by '/'s */
1622: <comment>\en ++line_num;
1623: <comment>"*"+"/" BEGIN(comment_caller);
1624: .Ed
1625: .Pp
1626: Furthermore, the current start condition can be accessed by using
1.1 deraadt 1627: the integer-valued
1.16 jmc 1628: .Dv YY_START
1629: macro.
1630: For example, the above assignments to
1631: .Em comment_caller
1.1 deraadt 1632: could instead be written
1.16 jmc 1633: .Pp
1634: .Dl comment_caller = YY_START;
1635: .Pp
1.1 deraadt 1636: Flex provides
1.16 jmc 1637: .Dv YYSTATE
1.1 deraadt 1638: as an alias for
1.16 jmc 1639: .Dv YY_START
1.36 schwarze 1640: (since that is what's used by
1641: .At
1.16 jmc 1642: .Nm lex ) .
1643: .Pp
1644: Note that start conditions do not have their own name-space;
1645: %s's and %x's declare names in the same fashion as #define's.
1646: .Pp
1.1 deraadt 1647: Finally, here's an example of how to match C-style quoted strings using
1.16 jmc 1648: exclusive start conditions, including expanded escape sequences
1649: (but not including checking for a string that's too long):
1650: .Bd -literal -offset indent
1651: %x str
1652:
1653: %%
1654: #define MAX_STR_CONST 1024
1655: char string_buf[MAX_STR_CONST];
1656: char *string_buf_ptr;
1657:
1658: \e" string_buf_ptr = string_buf; BEGIN(str);
1659:
1660: <str>\e" { /* saw closing quote - all done */
1661: BEGIN(INITIAL);
1662: *string_buf_ptr = '\e0';
1663: /*
1664: * return string constant token type and
1665: * value to parser
1666: */
1667: }
1668:
1669: <str>\en {
1670: /* error - unterminated string constant */
1671: /* generate error message */
1672: }
1673:
1674: <str>\e\e[0-7]{1,3} {
1675: /* octal escape sequence */
1676: int result;
1677:
1678: (void) sscanf(yytext + 1, "%o", &result);
1679:
1680: if (result > 0xff) {
1681: /* error, constant is out-of-bounds */
1682: } else
1683: *string_buf_ptr++ = result;
1684: }
1685:
1686: <str>\e\e[0-9]+ {
1687: /*
1688: * generate error - bad escape sequence; something
1689: * like '\e48' or '\e0777777'
1690: */
1691: }
1692:
1693: <str>\e\en *string_buf_ptr++ = '\en';
1694: <str>\e\et *string_buf_ptr++ = '\et';
1695: <str>\e\er *string_buf_ptr++ = '\er';
1696: <str>\e\eb *string_buf_ptr++ = '\eb';
1697: <str>\e\ef *string_buf_ptr++ = '\ef';
1698:
1699: <str>\e\e(.|\en) *string_buf_ptr++ = yytext[1];
1700:
1701: <str>[^\e\e\en\e"]+ {
1702: char *yptr = yytext;
1703:
1704: while (*yptr)
1705: *string_buf_ptr++ = *yptr++;
1706: }
1707: .Ed
1708: .Pp
1709: Often, such as in some of the examples above,
1710: a whole bunch of rules are all preceded by the same start condition(s).
1711: .Nm
1.1 deraadt 1712: makes this a little easier and cleaner by introducing a notion of
1713: start condition
1.16 jmc 1714: .Em scope .
1.1 deraadt 1715: A start condition scope is begun with:
1.16 jmc 1716: .Pp
1717: .Dl <SCs>{
1718: .Pp
1.1 deraadt 1719: where
1.16 jmc 1720: .Dq SCs
1721: is a list of one or more start conditions.
1722: Inside the start condition scope, every rule automatically has the prefix
1723: .Aq SCs
1.1 deraadt 1724: applied to it, until a
1.16 jmc 1725: .Sq }
1.1 deraadt 1726: which matches the initial
1.16 jmc 1727: .Sq { .
1.1 deraadt 1728: So, for example,
1.16 jmc 1729: .Bd -literal -offset indent
1730: <ESC>{
1731: "\e\en" return '\en';
1732: "\e\er" return '\er';
1733: "\e\ef" return '\ef';
1734: "\e\e0" return '\e0';
1735: }
1736: .Ed
1737: .Pp
1.1 deraadt 1738: is equivalent to:
1.16 jmc 1739: .Bd -literal -offset indent
1740: <ESC>"\e\en" return '\en';
1741: <ESC>"\e\er" return '\er';
1742: <ESC>"\e\ef" return '\ef';
1743: <ESC>"\e\e0" return '\e0';
1744: .Ed
1745: .Pp
1.1 deraadt 1746: Start condition scopes may be nested.
1.16 jmc 1747: .Pp
1.1 deraadt 1748: Three routines are available for manipulating stacks of start conditions:
1.16 jmc 1749: .Bl -tag -width Ds
1750: .It void yy_push_state(int new_state)
1751: Pushes the current start condition onto the top of the start condition
1.1 deraadt 1752: stack and switches to
1.16 jmc 1753: .Fa new_state
1754: as though
1755: .Dq BEGIN new_state
1756: had been used
1757: .Pq recall that start condition names are also integers .
1758: .It void yy_pop_state()
1759: Pops the top of the stack and switches to it via
1760: .Em BEGIN .
1761: .It int yy_top_state()
1762: Returns the top of the stack without altering the stack's contents.
1763: .El
1764: .Pp
1.1 deraadt 1765: The start condition stack grows dynamically and so has no built-in
1.16 jmc 1766: size limitation.
1767: If memory is exhausted, program execution aborts.
1768: .Pp
1769: To use start condition stacks, scanners must include a
1770: .Dq %option stack
1771: directive (see
1772: .Sx OPTIONS
1773: below).
1774: .Sh MULTIPLE INPUT BUFFERS
1775: Some scanners
1776: (such as those which support
1777: .Qq include
1778: files)
1779: require reading from several input streams.
1780: As
1781: .Nm
1.1 deraadt 1782: scanners do a large amount of buffering, one cannot control
1783: where the next input will be read from by simply writing a
1.16 jmc 1784: .Dv YY_INPUT
1.1 deraadt 1785: which is sensitive to the scanning context.
1.16 jmc 1786: .Dv YY_INPUT
1.1 deraadt 1787: is only called when the scanner reaches the end of its buffer, which
1.16 jmc 1788: may be a long time after scanning a statement such as an
1789: .Qq include
1.1 deraadt 1790: which requires switching the input source.
1.16 jmc 1791: .Pp
1.1 deraadt 1792: To negotiate these sorts of problems,
1.16 jmc 1793: .Nm
1.1 deraadt 1794: provides a mechanism for creating and switching between multiple
1.16 jmc 1795: input buffers.
1796: An input buffer is created by using:
1797: .Pp
1798: .D1 YY_BUFFER_STATE yy_create_buffer(FILE *file, int size)
1799: .Pp
1.1 deraadt 1800: which takes a
1.16 jmc 1801: .Fa FILE
1802: pointer and a
1803: .Fa size
1804: and creates a buffer associated with the given file and large enough to hold
1805: .Fa size
1.1 deraadt 1806: characters (when in doubt, use
1.16 jmc 1807: .Dv YY_BUF_SIZE
1808: for the size).
1809: It returns a
1810: .Dv YY_BUFFER_STATE
1811: handle, which may then be passed to other routines
1812: .Pq see below .
1813: The
1814: .Dv YY_BUFFER_STATE
1.1 deraadt 1815: type is a pointer to an opaque
1.16 jmc 1816: .Dq struct yy_buffer_state
1817: structure, so
1818: .Dv YY_BUFFER_STATE
1819: variables may be safely initialized to
1820: .Dq ((YY_BUFFER_STATE) 0)
1821: if desired, and the opaque structure can also be referred to in order to
1822: correctly declare input buffers in source files other than that of scanners.
1823: Note that the
1824: .Fa FILE
1.1 deraadt 1825: pointer in the call to
1.16 jmc 1826: .Fn yy_create_buffer
1.1 deraadt 1827: is only used as the value of
1.16 jmc 1828: .Fa yyin
1.1 deraadt 1829: seen by
1.16 jmc 1830: .Dv YY_INPUT ;
1831: if
1832: .Dv YY_INPUT
1833: is redefined so that it no longer uses
1834: .Fa yyin ,
1835: then a nil
1836: .Fa FILE
1837: pointer can safely be passed to
1838: .Fn yy_create_buffer .
1839: To select a particular buffer to scan:
1840: .Pp
1841: .D1 void yy_switch_to_buffer(YY_BUFFER_STATE new_buffer)
1842: .Pp
1843: It switches the scanner's input buffer so subsequent tokens will
1.1 deraadt 1844: come from
1.16 jmc 1845: .Fa new_buffer .
1.1 deraadt 1846: Note that
1.16 jmc 1847: .Fn yy_switch_to_buffer
1848: may be used by
1849: .Fn yywrap
1850: to set things up for continued scanning,
1851: instead of opening a new file and pointing
1852: .Fa yyin
1853: at it.
1854: Note also that switching input sources via either
1855: .Fn yy_switch_to_buffer
1856: or
1857: .Fn yywrap
1858: does not change the start condition.
1859: .Pp
1860: .D1 void yy_delete_buffer(YY_BUFFER_STATE buffer)
1861: .Pp
1862: is used to reclaim the storage associated with a buffer.
1863: .Pf ( Fa buffer
1.1 deraadt 1864: can be nil, in which case the routine does nothing.)
1.16 jmc 1865: To clear the current contents of a buffer:
1866: .Pp
1867: .D1 void yy_flush_buffer(YY_BUFFER_STATE buffer)
1868: .Pp
1.1 deraadt 1869: This function discards the buffer's contents,
1.16 jmc 1870: so the next time the scanner attempts to match a token from the buffer,
1871: it will first fill the buffer anew using
1872: .Dv YY_INPUT .
1873: .Pp
1874: .Fn yy_new_buffer
1.1 deraadt 1875: is an alias for
1.16 jmc 1876: .Fn yy_create_buffer ,
1.1 deraadt 1877: provided for compatibility with the C++ use of
1.16 jmc 1878: .Em new
1.1 deraadt 1879: and
1.16 jmc 1880: .Em delete
1.1 deraadt 1881: for creating and destroying dynamic objects.
1.16 jmc 1882: .Pp
1.1 deraadt 1883: Finally, the
1.16 jmc 1884: .Dv YY_CURRENT_BUFFER
1.1 deraadt 1885: macro returns a
1.16 jmc 1886: .Dv YY_BUFFER_STATE
1.1 deraadt 1887: handle to the current buffer.
1.16 jmc 1888: .Pp
1.1 deraadt 1889: Here is an example of using these features for writing a scanner
1890: which expands include files (the
1.16 jmc 1891: .Aq Aq EOF
1.1 deraadt 1892: feature is discussed below):
1.16 jmc 1893: .Bd -literal -offset indent
1894: /*
1895: * the "incl" state is used for picking up the name
1896: * of an include file
1897: */
1898: %x incl
1899:
1900: %{
1901: #define MAX_INCLUDE_DEPTH 10
1902: YY_BUFFER_STATE include_stack[MAX_INCLUDE_DEPTH];
1903: int include_stack_ptr = 0;
1904: %}
1905:
1906: %%
1907: include BEGIN(incl);
1908:
1909: [a-z]+ ECHO;
1910: [^a-z\en]*\en? ECHO;
1911:
1912: <incl>[ \et]* /* eat the whitespace */
1913: <incl>[^ \et\en]+ { /* got the include file name */
1914: if (include_stack_ptr >= MAX_INCLUDE_DEPTH)
1915: errx(1, "Includes nested too deeply");
1916:
1917: include_stack[include_stack_ptr++] =
1918: YY_CURRENT_BUFFER;
1919:
1920: yyin = fopen(yytext, "r");
1921:
1922: if (yyin == NULL)
1923: err(1, NULL);
1.1 deraadt 1924:
1.16 jmc 1925: yy_switch_to_buffer(
1926: yy_create_buffer(yyin, YY_BUF_SIZE));
1.1 deraadt 1927:
1.16 jmc 1928: BEGIN(INITIAL);
1929: }
1.1 deraadt 1930:
1.16 jmc 1931: <<EOF>> {
1932: if (--include_stack_ptr < 0)
1.1 deraadt 1933: yyterminate();
1.16 jmc 1934: else {
1935: yy_delete_buffer(YY_CURRENT_BUFFER);
1.1 deraadt 1936: yy_switch_to_buffer(
1.16 jmc 1937: include_stack[include_stack_ptr]);
1938: }
1939: }
1940: .Ed
1941: .Pp
1.1 deraadt 1942: Three routines are available for setting up input buffers for
1.16 jmc 1943: scanning in-memory strings instead of files.
1944: All of them create a new input buffer for scanning the string,
1945: and return a corresponding
1946: .Dv YY_BUFFER_STATE
1947: handle (which should be deleted afterwards using
1948: .Fn yy_delete_buffer ) .
1949: They also switch to the new buffer using
1950: .Fn yy_switch_to_buffer ,
1.1 deraadt 1951: so the next call to
1.16 jmc 1952: .Fn yylex
1.1 deraadt 1953: will start scanning the string.
1.16 jmc 1954: .Bl -tag -width Ds
1955: .It yy_scan_string(const char *str)
1956: Scans a NUL-terminated string.
1957: .It yy_scan_bytes(const char *bytes, int len)
1958: Scans
1959: .Fa len
1960: bytes
1961: .Pq including possibly NUL's
1.1 deraadt 1962: starting at location
1.16 jmc 1963: .Fa bytes .
1964: .El
1965: .Pp
1966: Note that both of these functions create and scan a copy
1967: of the string or bytes.
1968: (This may be desirable, since
1969: .Fn yylex
1970: modifies the contents of the buffer it is scanning.)
1971: The copy can be avoided by using:
1972: .Bl -tag -width Ds
1973: .It yy_scan_buffer(char *base, yy_size_t size)
1974: Which scans the buffer starting at
1975: .Fa base ,
1.1 deraadt 1976: consisting of
1.16 jmc 1977: .Fa size
1978: bytes, the last two bytes of which must be
1979: .Dv YY_END_OF_BUFFER_CHAR
1980: .Pq ASCII NUL .
1981: These last two bytes are not scanned; thus, scanning consists of
1982: base[0] through base[size-2], inclusive.
1983: .Pp
1984: If
1985: .Fa base
1986: is not set up in this manner
1987: (i.e., forget the final two
1988: .Dv YY_END_OF_BUFFER_CHAR
1.1 deraadt 1989: bytes), then
1.16 jmc 1990: .Fn yy_scan_buffer
1.1 deraadt 1991: returns a nil pointer instead of creating a new input buffer.
1.16 jmc 1992: .Pp
1.1 deraadt 1993: The type
1.16 jmc 1994: .Fa yy_size_t
1995: is an integral type which can be cast to an integer expression
1.1 deraadt 1996: reflecting the size of the buffer.
1.16 jmc 1997: .El
1998: .Sh END-OF-FILE RULES
1999: The special rule
2000: .Qq Aq Aq EOF
2001: indicates actions which are to be taken when an end-of-file is encountered and
2002: .Fn yywrap
2003: returns non-zero
2004: .Pq i.e., indicates no further files to process .
2005: The action must finish by doing one of four things:
2006: .Bl -dash
2007: .It
2008: Assigning
2009: .Em yyin
2010: to a new input file
2011: (in previous versions of
2012: .Nm ,
2013: after doing the assignment, it was necessary to call the special action
2014: .Dv YY_NEW_FILE ;
2015: this is no longer necessary).
2016: .It
2017: Executing a
2018: .Em return
2019: statement.
2020: .It
2021: Executing the special
2022: .Fn yyterminate
2023: action.
2024: .It
2025: Switching to a new buffer using
2026: .Fn yy_switch_to_buffer
1.1 deraadt 2027: as shown in the example above.
1.16 jmc 2028: .El
2029: .Pp
2030: .Aq Aq EOF
2031: rules may not be used with other patterns;
2032: they may only be qualified with a list of start conditions.
2033: If an unqualified
2034: .Aq Aq EOF
2035: rule is given, it applies to all start conditions which do not already have
2036: .Aq Aq EOF
2037: actions.
2038: To specify an
2039: .Aq Aq EOF
2040: rule for only the initial start condition, use
2041: .Pp
2042: .Dl <INITIAL><<EOF>>
2043: .Pp
1.1 deraadt 2044: These rules are useful for catching things like unclosed comments.
2045: An example:
1.16 jmc 2046: .Bd -literal -offset indent
2047: %x quote
2048: %%
2049:
2050: \&...other rules for dealing with quotes...
2051:
2052: <quote><<EOF>> {
2053: error("unterminated quote");
2054: yyterminate();
2055: }
2056: <<EOF>> {
2057: if (*++filelist)
2058: yyin = fopen(*filelist, "r");
2059: else
2060: yyterminate();
2061: }
2062: .Ed
2063: .Sh MISCELLANEOUS MACROS
1.1 deraadt 2064: The macro
1.16 jmc 2065: .Dv YY_USER_ACTION
1.1 deraadt 2066: can be defined to provide an action
1.16 jmc 2067: which is always executed prior to the matched rule's action.
2068: For example,
1.1 deraadt 2069: it could be #define'd to call a routine to convert yytext to lower-case.
2070: When
1.16 jmc 2071: .Dv YY_USER_ACTION
1.1 deraadt 2072: is invoked, the variable
1.16 jmc 2073: .Fa yy_act
2074: gives the number of the matched rule
2075: .Pq rules are numbered starting with 1 .
2076: For example, to profile how often each rule is matched,
2077: the following would do the trick:
2078: .Pp
2079: .Dl #define YY_USER_ACTION ++ctr[yy_act]
2080: .Pp
1.1 deraadt 2081: where
1.16 jmc 2082: .Fa ctr
2083: is an array to hold the counts for the different rules.
2084: Note that the macro
2085: .Dv YY_NUM_RULES
2086: gives the total number of rules
2087: (including the default rule, even if
2088: .Fl s
2089: is used),
1.1 deraadt 2090: so a correct declaration for
1.16 jmc 2091: .Fa ctr
1.1 deraadt 2092: is:
1.16 jmc 2093: .Pp
2094: .Dl int ctr[YY_NUM_RULES];
2095: .Pp
1.1 deraadt 2096: The macro
1.16 jmc 2097: .Dv YY_USER_INIT
1.1 deraadt 2098: may be defined to provide an action which is always executed before
1.16 jmc 2099: the first scan
2100: .Pq and before the scanner's internal initializations are done .
1.1 deraadt 2101: For example, it could be used to call a routine to read
2102: in a data table or open a logging file.
1.16 jmc 2103: .Pp
1.1 deraadt 2104: The macro
1.16 jmc 2105: .Dv yy_set_interactive(is_interactive)
1.1 deraadt 2106: can be used to control whether the current buffer is considered
1.16 jmc 2107: .Em interactive .
1.1 deraadt 2108: An interactive buffer is processed more slowly,
2109: but must be used when the scanner's input source is indeed
2110: interactive to avoid problems due to waiting to fill buffers
2111: (see the discussion of the
1.16 jmc 2112: .Fl I
2113: flag below).
2114: A non-zero value in the macro invocation marks the buffer as interactive,
2115: a zero value as non-interactive.
2116: Note that use of this macro overrides
2117: .Dq %option always-interactive
2118: or
2119: .Dq %option never-interactive
2120: (see
2121: .Sx OPTIONS
2122: below).
2123: .Fn yy_set_interactive
1.1 deraadt 2124: must be invoked prior to beginning to scan the buffer that is
1.16 jmc 2125: .Pq or is not
2126: to be considered interactive.
2127: .Pp
1.1 deraadt 2128: The macro
1.16 jmc 2129: .Dv yy_set_bol(at_bol)
1.1 deraadt 2130: can be used to control whether the current buffer's scanning
2131: context for the next token match is done as though at the
1.16 jmc 2132: beginning of a line.
2133: A non-zero macro argument makes rules anchored with
2134: .Sq ^
2135: active, while a zero argument makes
2136: .Sq ^
2137: rules inactive.
2138: .Pp
1.1 deraadt 2139: The macro
1.16 jmc 2140: .Dv YY_AT_BOL
2141: returns true if the next token scanned from the current buffer will have
2142: .Sq ^
2143: rules active, false otherwise.
2144: .Pp
1.1 deraadt 2145: In the generated scanner, the actions are all gathered in one large
2146: switch statement and separated using
1.16 jmc 2147: .Dv YY_BREAK ,
2148: which may be redefined.
2149: By default, it is simply a
2150: .Qq break ,
2151: to separate each rule's action from the following rules.
1.1 deraadt 2152: Redefining
1.16 jmc 2153: .Dv YY_BREAK
1.1 deraadt 2154: allows, for example, C++ users to
1.16 jmc 2155: .Dq #define YY_BREAK
2156: to do nothing
2157: (while being very careful that every rule ends with a
2158: .Qq break
2159: or a
2160: .Qq return ! )
2161: to avoid suffering from unreachable statement warnings where because a rule's
2162: action ends with
2163: .Dq return ,
2164: the
2165: .Dv YY_BREAK
1.1 deraadt 2166: is inaccessible.
1.16 jmc 2167: .Sh VALUES AVAILABLE TO THE USER
1.1 deraadt 2168: This section summarizes the various values available to the user
2169: in the rule actions.
1.16 jmc 2170: .Bl -tag -width Ds
2171: .It char *yytext
2172: Holds the text of the current token.
2173: It may be modified but not lengthened
2174: .Pq characters cannot be appended to the end .
2175: .Pp
1.1 deraadt 2176: If the special directive
1.16 jmc 2177: .Dq %array
1.1 deraadt 2178: appears in the first section of the scanner description, then
1.16 jmc 2179: .Fa yytext
1.1 deraadt 2180: is instead declared
1.16 jmc 2181: .Dq char yytext[YYLMAX] ,
1.1 deraadt 2182: where
1.16 jmc 2183: .Dv YYLMAX
2184: is a macro definition that can be redefined in the first section
2185: to change the default value
2186: .Pq generally 8KB .
2187: Using
2188: .Dq %array
1.1 deraadt 2189: results in somewhat slower scanners, but the value of
1.16 jmc 2190: .Fa yytext
1.1 deraadt 2191: becomes immune to calls to
1.16 jmc 2192: .Fn input
1.1 deraadt 2193: and
1.16 jmc 2194: .Fn unput ,
1.1 deraadt 2195: which potentially destroy its value when
1.16 jmc 2196: .Fa yytext
2197: is a character pointer.
2198: The opposite of
2199: .Dq %array
1.1 deraadt 2200: is
1.16 jmc 2201: .Dq %pointer ,
1.1 deraadt 2202: which is the default.
1.16 jmc 2203: .Pp
2204: .Dq %array
2205: cannot be used when generating C++ scanner classes
1.1 deraadt 2206: (the
1.16 jmc 2207: .Fl +
1.1 deraadt 2208: flag).
1.16 jmc 2209: .It int yyleng
2210: Holds the length of the current token.
2211: .It FILE *yyin
2212: Is the file which by default
2213: .Nm
2214: reads from.
2215: It may be redefined, but doing so only makes sense before
2216: scanning begins or after an
2217: .Dv EOF
2218: has been encountered.
2219: Changing it in the midst of scanning will have unexpected results since
2220: .Nm
1.1 deraadt 2221: buffers its input; use
1.16 jmc 2222: .Fn yyrestart
1.1 deraadt 2223: instead.
2224: Once scanning terminates because an end-of-file
1.16 jmc 2225: has been seen,
2226: .Fa yyin
2227: can be assigned as the new input file
2228: and the scanner can be called again to continue scanning.
2229: .It void yyrestart(FILE *new_file)
2230: May be called to point
2231: .Fa yyin
2232: at the new input file.
2233: The switch-over to the new file is immediate
2234: .Pq any previously buffered-up input is lost .
2235: Note that calling
2236: .Fn yyrestart
1.1 deraadt 2237: with
1.16 jmc 2238: .Fa yyin
1.1 deraadt 2239: as an argument thus throws away the current input buffer and continues
2240: scanning the same input file.
1.16 jmc 2241: .It FILE *yyout
2242: Is the file to which
2243: .Em ECHO
2244: actions are done.
2245: It can be reassigned by the user.
2246: .It YY_CURRENT_BUFFER
2247: Returns a
2248: .Dv YY_BUFFER_STATE
1.1 deraadt 2249: handle to the current buffer.
1.16 jmc 2250: .It YY_START
2251: Returns an integer value corresponding to the current start condition.
2252: This value can subsequently be used with
2253: .Em BEGIN
1.1 deraadt 2254: to return to that start condition.
1.16 jmc 2255: .El
2256: .Sh INTERFACING WITH YACC
1.1 deraadt 2257: One of the main uses of
1.16 jmc 2258: .Nm
1.1 deraadt 2259: is as a companion to the
1.16 jmc 2260: .Xr yacc 1
1.1 deraadt 2261: parser-generator.
1.16 jmc 2262: yacc parsers expect to call a routine named
2263: .Fn yylex
2264: to find the next input token.
2265: The routine is supposed to return the type of the next token
2266: as well as putting any associated value in the global
1.17 jmc 2267: .Fa yylval ,
2268: which is defined externally,
2269: and can be a union or any other complex data structure.
1.1 deraadt 2270: To use
1.16 jmc 2271: .Nm
2272: with yacc, one specifies the
2273: .Fl d
2274: option to yacc to instruct it to generate the file
2275: .Pa y.tab.h
1.1 deraadt 2276: containing definitions of all the
1.16 jmc 2277: .Dq %tokens
2278: appearing in the yacc input.
2279: This file is then included in the
2280: .Nm
2281: scanner.
2282: For example, if one of the tokens is
2283: .Qq TOK_NUMBER ,
1.1 deraadt 2284: part of the scanner might look like:
1.16 jmc 2285: .Bd -literal -offset indent
2286: %{
2287: #include "y.tab.h"
2288: %}
2289:
2290: %%
2291:
2292: [0-9]+ yylval = atoi(yytext); return TOK_NUMBER;
2293: .Ed
2294: .Sh OPTIONS
2295: .Nm
1.1 deraadt 2296: has the following options:
1.16 jmc 2297: .Bl -tag -width Ds
2298: .It Fl 7
2299: Instructs
2300: .Nm
2301: to generate a 7-bit scanner, i.e., one which can only recognize 7-bit
2302: characters in its input.
2303: The advantage of using
2304: .Fl 7
1.1 deraadt 2305: is that the scanner's tables can be up to half the size of those generated
2306: using the
1.16 jmc 2307: .Fl 8
2308: option
2309: .Pq see below .
2310: The disadvantage is that such scanners often hang
1.1 deraadt 2311: or crash if their input contains an 8-bit character.
1.16 jmc 2312: .Pp
2313: Note, however, that unless generating a scanner using the
2314: .Fl Cf
1.1 deraadt 2315: or
1.16 jmc 2316: .Fl CF
1.1 deraadt 2317: table compression options, use of
1.16 jmc 2318: .Fl 7
2319: will save only a small amount of table space,
2320: and make the scanner considerably less portable.
2321: .Nm flex Ns 's
2322: default behavior is to generate an 8-bit scanner unless
2323: .Fl Cf
2324: or
2325: .Fl CF
2326: is specified, in which case
2327: .Nm
2328: defaults to generating 7-bit scanners unless it was
2329: configured to generate 8-bit scanners
2330: (as will often be the case with non-USA sites).
2331: It is possible tell whether
2332: .Nm
2333: generated a 7-bit or an 8-bit scanner by inspecting the flag summary in the
2334: .Fl v
2335: output as described below.
2336: .Pp
2337: Note that if
2338: .Fl Cfe
2339: or
2340: .Fl CFe
2341: are used
2342: (the table compression options, but also using equivalence classes as
2343: discussed below),
2344: .Nm
2345: still defaults to generating an 8-bit scanner,
2346: since usually with these compression options full 8-bit tables
1.1 deraadt 2347: are not much more expensive than 7-bit tables.
1.16 jmc 2348: .It Fl 8
2349: Instructs
2350: .Nm
1.1 deraadt 2351: to generate an 8-bit scanner, i.e., one which can recognize 8-bit
1.16 jmc 2352: characters.
2353: This flag is only needed for scanners generated using
2354: .Fl Cf
1.1 deraadt 2355: or
1.16 jmc 2356: .Fl CF ,
2357: as otherwise
2358: .Nm
2359: defaults to generating an 8-bit scanner anyway.
2360: .Pp
1.1 deraadt 2361: See the discussion of
1.16 jmc 2362: .Fl 7
2363: above for
2364: .Nm flex Ns 's
2365: default behavior and the tradeoffs between 7-bit and 8-bit scanners.
2366: .It Fl B
2367: Instructs
2368: .Nm
2369: to generate a
2370: .Em batch
2371: scanner, the opposite of
2372: .Em interactive
2373: scanners generated by
2374: .Fl I
2375: .Pq see below .
2376: In general,
2377: .Fl B
2378: is used when the scanner will never be used interactively,
2379: and you want to squeeze a little more performance out of it.
2380: If the aim is instead to squeeze out a lot more performance,
2381: use the
2382: .Fl Cf
2383: or
2384: .Fl CF
2385: options
2386: .Pq discussed below ,
2387: which turn on
2388: .Fl B
2389: automatically anyway.
2390: .It Fl b
2391: Generate backing-up information to
2392: .Pa lex.backup .
2393: This is a list of scanner states which require backing up
2394: and the input characters on which they do so.
2395: By adding rules one can remove backing-up states.
2396: If all backing-up states are eliminated and
2397: .Fl Cf
2398: or
2399: .Fl CF
2400: is used, the generated scanner will run faster (see the
2401: .Fl p
2402: flag).
2403: Only users who wish to squeeze every last cycle out of their
2404: scanners need worry about this option.
2405: (See the section on
2406: .Sx PERFORMANCE CONSIDERATIONS
2407: below.)
2408: .It Fl C Ns Op Cm aeFfmr
2409: Controls the degree of table compression and, more generally, trade-offs
1.1 deraadt 2410: between small scanners and fast scanners.
1.16 jmc 2411: .Bl -tag -width Ds
2412: .It Fl Ca
2413: Instructs
2414: .Nm
2415: to trade off larger tables in the generated scanner for faster performance
2416: because the elements of the tables are better aligned for memory access
2417: and computation.
2418: On some
2419: .Tn RISC
2420: architectures, fetching and manipulating longwords is more efficient
2421: than with smaller-sized units such as shortwords.
2422: This option can double the size of the tables used by the scanner.
2423: .It Fl Ce
2424: Directs
2425: .Nm
1.1 deraadt 2426: to construct
1.16 jmc 2427: .Em equivalence classes ,
2428: i.e., sets of characters which have identical lexical properties
2429: (for example, if the only appearance of digits in the
2430: .Nm
1.1 deraadt 2431: input is in the character class
1.16 jmc 2432: .Qq [0-9]
2433: then the digits
2434: .Sq 0 ,
2435: .Sq 1 ,
2436: .Sq ... ,
2437: .Sq 9
2438: will all be put in the same equivalence class).
2439: Equivalence classes usually give dramatic reductions in the final
2440: table/object file sizes
2441: .Pq typically a factor of 2\-5
2442: and are pretty cheap performance-wise
2443: .Pq one array look-up per character scanned .
2444: .It Fl CF
2445: Specifies that the alternate fast scanner representation
2446: (described below under the
2447: .Fl F
2448: option)
2449: should be used.
2450: This option cannot be used with
2451: .Fl + .
2452: .It Fl Cf
2453: Specifies that the
2454: .Em full
2455: scanner tables should be generated \-
2456: .Nm
2457: should not compress the tables by taking advantage of
2458: similar transition functions for different states.
2459: .It Fl \&Cm
2460: Directs
2461: .Nm
1.1 deraadt 2462: to construct
1.16 jmc 2463: .Em meta-equivalence classes ,
2464: which are sets of equivalence classes
2465: (or characters, if equivalence classes are not being used)
2466: that are commonly used together.
2467: Meta-equivalence classes are often a big win when using compressed tables,
2468: but they have a moderate performance impact
2469: (one or two
2470: .Qq if
2471: tests and one array look-up per character scanned).
2472: .It Fl Cr
2473: Causes the generated scanner to
2474: .Em bypass
2475: use of the standard I/O library
2476: .Pq stdio
2477: for input.
2478: Instead of calling
2479: .Xr fread 3
1.1 deraadt 2480: or
1.16 jmc 2481: .Xr getc 3 ,
1.1 deraadt 2482: the scanner will use the
1.16 jmc 2483: .Xr read 2
2484: system call,
2485: resulting in a performance gain which varies from system to system,
2486: but in general is probably negligible unless
2487: .Fl Cf
1.1 deraadt 2488: or
1.16 jmc 2489: .Fl CF
2490: are being used.
1.1 deraadt 2491: Using
1.16 jmc 2492: .Fl Cr
2493: can cause strange behavior if, for example, reading from
2494: .Fa yyin
2495: using stdio prior to calling the scanner
2496: (because the scanner will miss whatever text previous reads left
2497: in the stdio input buffer).
2498: .Pp
2499: .Fl Cr
2500: has no effect if
2501: .Dv YY_INPUT
2502: is defined
2503: (see
2504: .Sx THE GENERATED SCANNER
2505: above).
2506: .El
2507: .Pp
1.1 deraadt 2508: A lone
1.16 jmc 2509: .Fl C
1.1 deraadt 2510: specifies that the scanner tables should be compressed but neither
2511: equivalence classes nor meta-equivalence classes should be used.
1.16 jmc 2512: .Pp
1.1 deraadt 2513: The options
1.16 jmc 2514: .Fl Cf
1.1 deraadt 2515: or
1.16 jmc 2516: .Fl CF
1.1 deraadt 2517: and
1.16 jmc 2518: .Fl \&Cm
2519: do not make sense together \- there is no opportunity for meta-equivalence
2520: classes if the table is not being compressed.
2521: Otherwise the options may be freely mixed, and are cumulative.
2522: .Pp
1.1 deraadt 2523: The default setting is
1.16 jmc 2524: .Fl Cem
1.1 deraadt 2525: which specifies that
1.16 jmc 2526: .Nm
2527: should generate equivalence classes and meta-equivalence classes.
2528: This setting provides the highest degree of table compression.
2529: It is possible to trade off faster-executing scanners at the cost of
2530: larger tables with the following generally being true:
2531: .Bd -unfilled -offset indent
2532: slowest & smallest
2533: -Cem
2534: -Cm
2535: -Ce
2536: -C
2537: -C{f,F}e
2538: -C{f,F}
2539: -C{f,F}a
2540: fastest & largest
2541: .Ed
2542: .Pp
1.1 deraadt 2543: Note that scanners with the smallest tables are usually generated and
1.16 jmc 2544: compiled the quickest,
2545: so during development the default is usually best,
2546: maximal compression.
2547: .Pp
2548: .Fl Cfe
2549: is often a good compromise between speed and size for production scanners.
2550: .It Fl d
2551: Makes the generated scanner run in debug mode.
2552: Whenever a pattern is recognized and the global
2553: .Fa yy_flex_debug
2554: is non-zero
2555: .Pq which is the default ,
2556: the scanner will write to stderr a line of the form:
2557: .Pp
2558: .D1 --accepting rule at line 53 ("the matched text")
2559: .Pp
2560: The line number refers to the location of the rule in the file
2561: defining the scanner
2562: (i.e., the file that was fed to
2563: .Nm ) .
2564: Messages are also generated when the scanner backs up,
2565: accepts the default rule,
2566: reaches the end of its input buffer
2567: (or encounters a NUL;
2568: at this point, the two look the same as far as the scanner's concerned),
2569: or reaches an end-of-file.
2570: .It Fl F
2571: Specifies that the fast scanner table representation should be used
2572: .Pq and stdio bypassed .
2573: This representation is about as fast as the full table representation
2574: .Pq Fl f ,
2575: and for some sets of patterns will be considerably smaller
2576: .Pq and for others, larger .
2577: In general, if the pattern set contains both
2578: .Qq keywords
2579: and a catch-all,
2580: .Qq identifier
2581: rule, such as in the set:
2582: .Bd -unfilled -offset indent
2583: "case" return TOK_CASE;
2584: "switch" return TOK_SWITCH;
2585: \&...
2586: "default" return TOK_DEFAULT;
2587: [a-z]+ return TOK_ID;
2588: .Ed
2589: .Pp
2590: then it's better to use the full table representation.
2591: If only the
2592: .Qq identifier
2593: rule is present and a hash table or some such is used to detect the keywords,
2594: it's better to use
2595: .Fl F .
2596: .Pp
2597: This option is equivalent to
2598: .Fl CFr
2599: .Pq see above .
2600: It cannot be used with
2601: .Fl + .
2602: .It Fl f
2603: Specifies
2604: .Em fast scanner .
2605: No table compression is done and stdio is bypassed.
2606: The result is large but fast.
2607: This option is equivalent to
2608: .Fl Cfr
2609: .Pq see above .
2610: .It Fl h
2611: Generates a help summary of
2612: .Nm flex Ns 's
2613: options to stdout and then exits.
2614: .Fl ?\&
2615: and
2616: .Fl Fl help
2617: are synonyms for
2618: .Fl h .
2619: .It Fl I
2620: Instructs
2621: .Nm
2622: to generate an
2623: .Em interactive
2624: scanner.
2625: An interactive scanner is one that only looks ahead to decide
2626: what token has been matched if it absolutely must.
2627: It turns out that always looking one extra character ahead,
2628: even if the scanner has already seen enough text
2629: to disambiguate the current token, is a bit faster than
2630: only looking ahead when necessary.
2631: But scanners that always look ahead give dreadful interactive performance;
2632: for example, when a user types a newline,
2633: it is not recognized as a newline token until they enter
2634: .Em another
2635: token, which often means typing in another whole line.
2636: .Pp
2637: .Nm
2638: scanners default to
2639: .Em interactive
2640: unless
2641: .Fl Cf
2642: or
2643: .Fl CF
2644: table-compression options are specified
2645: .Pq see above .
2646: That's because if high-performance is most important,
2647: one of these options should be used,
2648: so if they weren't,
2649: .Nm
1.24 sobrado 2650: assumes it is preferable to trade off a bit of run-time performance for
1.16 jmc 2651: intuitive interactive behavior.
2652: Note also that
2653: .Fl I
2654: cannot be used in conjunction with
2655: .Fl Cf
2656: or
2657: .Fl CF .
2658: Thus, this option is not really needed; it is on by default for all those
2659: cases in which it is allowed.
2660: .Pp
2661: A scanner can be forced to not be interactive by using
2662: .Fl B
2663: .Pq see above .
2664: .It Fl i
2665: Instructs
2666: .Nm
2667: to generate a case-insensitive scanner.
2668: The case of letters given in the
2669: .Nm
2670: input patterns will be ignored,
2671: and tokens in the input will be matched regardless of case.
2672: The matched text given in
2673: .Fa yytext
2674: will have the preserved case
2675: .Pq i.e., it will not be folded .
2676: .It Fl L
2677: Instructs
2678: .Nm
2679: not to generate
2680: .Dq #line
2681: directives.
2682: Without this option,
2683: .Nm
2684: peppers the generated scanner with #line directives so error messages
2685: in the actions will be correctly located with respect to either the original
2686: .Nm
2687: input file
2688: (if the errors are due to code in the input file),
2689: or
2690: .Pa lex.yy.c
2691: (if the errors are
2692: .Nm flex Ns 's
2693: fault \- these sorts of errors should be reported to the email address
2694: given below).
2695: .It Fl l
1.36 schwarze 2696: Turns on maximum compatibility with the original
2697: .At
1.16 jmc 2698: .Nm lex
2699: implementation.
2700: Note that this does not mean full compatibility.
2701: Use of this option costs a considerable amount of performance,
2702: and it cannot be used with the
2703: .Fl + , f , F , Cf ,
2704: or
2705: .Fl CF
2706: options.
2707: For details on the compatibilities it provides, see the section
2708: .Sx INCOMPATIBILITIES WITH LEX AND POSIX
2709: below.
2710: This option also results in the name
2711: .Dv YY_FLEX_LEX_COMPAT
2712: being #define'd in the generated scanner.
2713: .It Fl n
2714: Another do-nothing, deprecated option included only for
2715: .Tn POSIX
2716: compliance.
2717: .It Fl o Ns Ar output
2718: Directs
2719: .Nm
2720: to write the scanner to the file
2721: .Ar output
1.1 deraadt 2722: instead of
1.16 jmc 2723: .Pa lex.yy.c .
2724: If
2725: .Fl o
2726: is combined with the
2727: .Fl t
2728: option, then the scanner is written to stdout but its
2729: .Dq #line
2730: directives
2731: (see the
2732: .Fl L
2733: option above)
2734: refer to the file
2735: .Ar output .
2736: .It Fl P Ns Ar prefix
2737: Changes the default
2738: .Qq yy
1.1 deraadt 2739: prefix used by
1.16 jmc 2740: .Nm
1.6 aaron 2741: for all globally visible variable and function names to instead be
1.16 jmc 2742: .Ar prefix .
1.1 deraadt 2743: For example,
1.16 jmc 2744: .Fl P Ns Ar foo
1.1 deraadt 2745: changes the name of
1.16 jmc 2746: .Fa yytext
1.1 deraadt 2747: to
1.16 jmc 2748: .Fa footext .
1.1 deraadt 2749: It also changes the name of the default output file from
1.16 jmc 2750: .Pa lex.yy.c
1.1 deraadt 2751: to
1.16 jmc 2752: .Pa lex.foo.c .
1.1 deraadt 2753: Here are all of the names affected:
1.16 jmc 2754: .Bd -unfilled -offset indent
2755: yy_create_buffer
2756: yy_delete_buffer
2757: yy_flex_debug
2758: yy_init_buffer
2759: yy_flush_buffer
2760: yy_load_buffer_state
2761: yy_switch_to_buffer
2762: yyin
2763: yyleng
2764: yylex
2765: yylineno
2766: yyout
2767: yyrestart
2768: yytext
2769: yywrap
2770: .Ed
2771: .Pp
2772: (If using a C++ scanner, then only
2773: .Fa yywrap
1.1 deraadt 2774: and
1.16 jmc 2775: .Fa yyFlexLexer
1.1 deraadt 2776: are affected.)
1.16 jmc 2777: Within the scanner itself, it is still possible to refer to the global variables
1.1 deraadt 2778: and functions using either version of their name; but externally, they
2779: have the modified name.
1.16 jmc 2780: .Pp
2781: This option allows multiple
2782: .Nm
2783: programs to be easily linked together into the same executable.
2784: Note, though, that using this option also renames
2785: .Fn yywrap ,
2786: so now either an
2787: .Pq appropriately named
2788: version of the routine for the scanner must be supplied, or
2789: .Dq %option noyywrap
2790: must be used, as linking with
2791: .Fl lfl
2792: no longer provides one by default.
2793: .It Fl p
2794: Generates a performance report to stderr.
2795: The report consists of comments regarding features of the
2796: .Nm
2797: input file which will cause a serious loss of performance in the resulting
2798: scanner.
2799: If the flag is specified twice,
2800: comments regarding features that lead to minor performance losses
2801: will also be reported>
2802: .Pp
2803: Note that the use of
2804: .Em REJECT ,
2805: .Dq %option yylineno ,
2806: and variable trailing context
2807: (see the
2808: .Sx BUGS
2809: section below)
2810: entails a substantial performance penalty; use of
2811: .Fn yymore ,
2812: the
2813: .Sq ^
2814: operator, and the
2815: .Fl I
2816: flag entail minor performance penalties.
2817: .It Fl S Ns Ar skeleton
2818: Overrides the default skeleton file from which
2819: .Nm
2820: constructs its scanners.
2821: This option is needed only for
2822: .Nm
1.1 deraadt 2823: maintenance or development.
1.16 jmc 2824: .It Fl s
2825: Causes the default rule
2826: .Pq that unmatched scanner input is echoed to stdout
2827: to be suppressed.
2828: If the scanner encounters input that does not
2829: match any of its rules, it aborts with an error.
2830: This option is useful for finding holes in a scanner's rule set.
2831: .It Fl T
2832: Makes
2833: .Nm
2834: run in
2835: .Em trace
2836: mode.
2837: It will generate a lot of messages to stderr concerning
2838: the form of the input and the resultant non-deterministic and deterministic
2839: finite automata.
2840: This option is mostly for use in maintaining
2841: .Nm .
2842: .It Fl t
2843: Instructs
2844: .Nm
2845: to write the scanner it generates to standard output instead of
2846: .Pa lex.yy.c .
2847: .It Fl V
2848: Prints the version number to stdout and exits.
2849: .Fl Fl version
2850: is a synonym for
2851: .Fl V .
2852: .It Fl v
2853: Specifies that
2854: .Nm
2855: should write to stderr
2856: a summary of statistics regarding the scanner it generates.
2857: Most of the statistics are meaningless to the casual
2858: .Nm
2859: user, but the first line identifies the version of
2860: .Nm
2861: (same as reported by
2862: .Fl V ) ,
2863: and the next line the flags used when generating the scanner,
2864: including those that are on by default.
2865: .It Fl w
2866: Suppresses warning messages.
2867: .It Fl +
2868: Specifies that
2869: .Nm
2870: should generate a C++ scanner class.
2871: See the section on
2872: .Sx GENERATING C++ SCANNERS
2873: below for details.
2874: .El
2875: .Pp
2876: .Nm
1.1 deraadt 2877: also provides a mechanism for controlling options within the
1.16 jmc 2878: scanner specification itself, rather than from the
2879: .Nm
1.33 jmc 2880: command line.
1.1 deraadt 2881: This is done by including
1.16 jmc 2882: .Dq %option
1.1 deraadt 2883: directives in the first section of the scanner specification.
1.16 jmc 2884: Multiple options can be specified with a single
2885: .Dq %option
2886: directive, and multiple directives in the first section of the
2887: .Nm
2888: input file.
2889: .Pp
2890: Most options are given simply as names, optionally preceded by the word
2891: .Qq no
2892: .Pq with no intervening whitespace
2893: to negate their meaning.
2894: A number are equivalent to
2895: .Nm
2896: flags or their negation:
2897: .Bd -unfilled -offset indent
2898: 7bit -7 option
2899: 8bit -8 option
2900: align -Ca option
2901: backup -b option
2902: batch -B option
2903: c++ -+ option
2904:
2905: caseful or
2906: case-sensitive opposite of -i (default)
2907:
2908: case-insensitive or
2909: caseless -i option
2910:
2911: debug -d option
2912: default opposite of -s option
2913: ecs -Ce option
2914: fast -F option
2915: full -f option
2916: interactive -I option
2917: lex-compat -l option
2918: meta-ecs -Cm option
2919: perf-report -p option
2920: read -Cr option
2921: stdout -t option
2922: verbose -v option
2923: warn opposite of -w option
2924: (use "%option nowarn" for -w)
2925:
2926: array equivalent to "%array"
2927: pointer equivalent to "%pointer" (default)
2928: .Ed
2929: .Pp
2930: Some %option's provide features otherwise not available:
2931: .Bl -tag -width Ds
2932: .It always-interactive
2933: Instructs
2934: .Nm
2935: to generate a scanner which always considers its input
2936: .Qq interactive .
2937: Normally, on each new input file the scanner calls
2938: .Fn isatty
2939: in an attempt to determine whether the scanner's input source is interactive
2940: and thus should be read a character at a time.
2941: When this option is used, however, no such call is made.
2942: .It main
2943: Directs
2944: .Nm
2945: to provide a default
2946: .Fn main
1.1 deraadt 2947: program for the scanner, which simply calls
1.16 jmc 2948: .Fn yylex .
1.1 deraadt 2949: This option implies
1.16 jmc 2950: .Dq noyywrap
2951: .Pq see below .
2952: .It never-interactive
2953: Instructs
2954: .Nm
2955: to generate a scanner which never considers its input
2956: .Qq interactive
2957: (again, no call made to
2958: .Fn isatty ) .
1.1 deraadt 2959: This is the opposite of
1.16 jmc 2960: .Dq always-interactive .
2961: .It stack
2962: Enables the use of start condition stacks
2963: (see
2964: .Sx START CONDITIONS
2965: above).
2966: .It stdinit
2967: If set (i.e.,
2968: .Dq %option stdinit ) ,
1.1 deraadt 2969: initializes
1.16 jmc 2970: .Fa yyin
1.1 deraadt 2971: and
1.16 jmc 2972: .Fa yyout
2973: to stdin and stdout, instead of the default of
2974: .Dq nil .
1.1 deraadt 2975: Some existing
1.16 jmc 2976: .Nm lex
2977: programs depend on this behavior, even though it is not compliant with ANSI C,
2978: which does not require stdin and stdout to be compile-time constant.
2979: .It yylineno
2980: Directs
2981: .Nm
1.1 deraadt 2982: to generate a scanner that maintains the number of the current line
2983: read from its input in the global variable
1.16 jmc 2984: .Fa yylineno .
1.1 deraadt 2985: This option is implied by
1.16 jmc 2986: .Dq %option lex-compat .
2987: .It yywrap
2988: If unset (i.e.,
2989: .Dq %option noyywrap ) ,
1.1 deraadt 2990: makes the scanner not call
1.16 jmc 2991: .Fn yywrap
2992: upon an end-of-file, but simply assume that there are no more files to scan
2993: (until the user points
2994: .Fa yyin
1.1 deraadt 2995: at a new file and calls
1.16 jmc 2996: .Fn yylex
1.1 deraadt 2997: again).
1.16 jmc 2998: .El
2999: .Pp
3000: .Nm
3001: scans rule actions to determine whether the
3002: .Em REJECT
3003: or
3004: .Fn yymore
3005: features are being used.
3006: The
3007: .Dq reject
1.1 deraadt 3008: and
1.16 jmc 3009: .Dq yymore
3010: options are available to override its decision as to whether to use the
1.1 deraadt 3011: options, either by setting them (e.g.,
1.16 jmc 3012: .Dq %option reject )
3013: to indicate the feature is indeed used,
3014: or unsetting them to indicate it actually is not used
1.1 deraadt 3015: (e.g.,
1.16 jmc 3016: .Dq %option noyymore ) .
3017: .Pp
3018: Three options take string-delimited values, offset with
3019: .Sq = :
3020: .Pp
3021: .D1 %option outfile="ABC"
3022: .Pp
1.1 deraadt 3023: is equivalent to
1.16 jmc 3024: .Fl o Ns Ar ABC ,
1.1 deraadt 3025: and
1.16 jmc 3026: .Pp
3027: .D1 %option prefix="XYZ"
3028: .Pp
1.1 deraadt 3029: is equivalent to
1.16 jmc 3030: .Fl P Ns Ar XYZ .
1.1 deraadt 3031: Finally,
1.16 jmc 3032: .Pp
3033: .D1 %option yyclass="foo"
3034: .Pp
3035: only applies when generating a C++ scanner
3036: .Pf ( Fl +
3037: option).
3038: It informs
3039: .Nm
3040: that
3041: .Dq foo
3042: has been derived as a subclass of yyFlexLexer, so
3043: .Nm
3044: will place actions in the member function
3045: .Dq foo::yylex()
1.1 deraadt 3046: instead of
1.16 jmc 3047: .Dq yyFlexLexer::yylex() .
1.1 deraadt 3048: It also generates a
1.16 jmc 3049: .Dq yyFlexLexer::yylex()
1.1 deraadt 3050: member function that emits a run-time error (by invoking
1.16 jmc 3051: .Dq yyFlexLexer::LexerError() )
1.1 deraadt 3052: if called.
1.16 jmc 3053: See
3054: .Sx GENERATING C++ SCANNERS ,
3055: below, for additional information.
3056: .Pp
3057: A number of options are available for
1.32 jmc 3058: lint
1.16 jmc 3059: purists who want to suppress the appearance of unneeded routines
3060: in the generated scanner.
3061: Each of the following, if unset
1.1 deraadt 3062: (e.g.,
1.16 jmc 3063: .Dq %option nounput ) ,
3064: results in the corresponding routine not appearing in the generated scanner:
3065: .Bd -unfilled -offset indent
3066: input, unput
3067: yy_push_state, yy_pop_state, yy_top_state
3068: yy_scan_buffer, yy_scan_bytes, yy_scan_string
3069: .Ed
3070: .Pp
1.1 deraadt 3071: (though
1.16 jmc 3072: .Fn yy_push_state
3073: and friends won't appear anyway unless
3074: .Dq %option stack
3075: is being used).
3076: .Sh PERFORMANCE CONSIDERATIONS
1.1 deraadt 3077: The main design goal of
1.16 jmc 3078: .Nm
3079: is that it generate high-performance scanners.
3080: It has been optimized for dealing well with large sets of rules.
3081: Aside from the effects on scanner speed of the table compression
3082: .Fl C
1.1 deraadt 3083: options outlined above,
1.16 jmc 3084: there are a number of options/actions which degrade performance.
3085: These are, from most expensive to least:
3086: .Bd -unfilled -offset indent
3087: REJECT
3088: %option yylineno
3089: arbitrary trailing context
3090:
3091: pattern sets that require backing up
3092: %array
3093: %option interactive
3094: %option always-interactive
3095:
3096: \&'^' beginning-of-line operator
3097: yymore()
3098: .Ed
3099: .Pp
3100: with the first three all being quite expensive
3101: and the last two being quite cheap.
3102: Note also that
3103: .Fn unput
3104: is implemented as a routine call that potentially does quite a bit of work,
3105: while
3106: .Fn yyless
3107: is a quite-cheap macro; so if just putting back some excess text,
3108: use
3109: .Fn yyless .
3110: .Pp
3111: .Em REJECT
1.1 deraadt 3112: should be avoided at all costs when performance is important.
3113: It is a particularly expensive option.
1.16 jmc 3114: .Pp
1.1 deraadt 3115: Getting rid of backing up is messy and often may be an enormous
1.16 jmc 3116: amount of work for a complicated scanner.
3117: In principal, one begins by using the
3118: .Fl b
1.1 deraadt 3119: flag to generate a
1.16 jmc 3120: .Pa lex.backup
3121: file.
3122: For example, on the input
3123: .Bd -literal -offset indent
3124: %%
3125: foo return TOK_KEYWORD;
3126: foobar return TOK_KEYWORD;
3127: .Ed
3128: .Pp
1.1 deraadt 3129: the file looks like:
1.16 jmc 3130: .Bd -literal -offset indent
3131: State #6 is non-accepting -
3132: associated rule line numbers:
3133: 2 3
3134: out-transitions: [ o ]
3135: jam-transitions: EOF [ \e001-n p-\e177 ]
3136:
3137: State #8 is non-accepting -
3138: associated rule line numbers:
3139: 3
3140: out-transitions: [ a ]
3141: jam-transitions: EOF [ \e001-` b-\e177 ]
3142:
3143: State #9 is non-accepting -
3144: associated rule line numbers:
3145: 3
3146: out-transitions: [ r ]
3147: jam-transitions: EOF [ \e001-q s-\e177 ]
3148:
3149: Compressed tables always back up.
3150: .Ed
3151: .Pp
1.1 deraadt 3152: The first few lines tell us that there's a scanner state in
1.16 jmc 3153: which it can make a transition on an
3154: .Sq o
3155: but not on any other character,
3156: and that in that state the currently scanned text does not match any rule.
3157: The state occurs when trying to match the rules found
1.1 deraadt 3158: at lines 2 and 3 in the input file.
1.16 jmc 3159: If the scanner is in that state and then reads something other than an
3160: .Sq o ,
3161: it will have to back up to find a rule which is matched.
3162: With a bit of headscratching one can see that this must be the
3163: state it's in when it has seen
3164: .Sq fo .
3165: When this has happened, if anything other than another
3166: .Sq o
3167: is seen, the scanner will have to back up to simply match the
3168: .Sq f
3169: .Pq by the default rule .
3170: .Pp
3171: The comment regarding State #8 indicates there's a problem when
3172: .Qq foob
3173: has been scanned.
3174: Indeed, on any character other than an
3175: .Sq a ,
3176: the scanner will have to back up to accept
3177: .Qq foo .
3178: Similarly, the comment for State #9 concerns when
3179: .Qq fooba
3180: has been scanned and an
3181: .Sq r
3182: does not follow.
3183: .Pp
1.1 deraadt 3184: The final comment reminds us that there's no point going to
1.16 jmc 3185: all the trouble of removing backing up from the rules unless we're using
3186: .Fl Cf
1.1 deraadt 3187: or
1.16 jmc 3188: .Fl CF ,
1.1 deraadt 3189: since there's no performance gain doing so with compressed scanners.
1.16 jmc 3190: .Pp
3191: The way to remove the backing up is to add
3192: .Qq error
3193: rules:
3194: .Bd -literal -offset indent
3195: %%
3196: foo return TOK_KEYWORD;
3197: foobar return TOK_KEYWORD;
3198:
3199: fooba |
3200: foob |
3201: fo {
3202: /* false alarm, not really a keyword */
3203: return TOK_ID;
3204: }
3205: .Ed
3206: .Pp
3207: Eliminating backing up among a list of keywords can also be done using a
3208: .Qq catch-all
3209: rule:
3210: .Bd -literal -offset indent
3211: %%
3212: foo return TOK_KEYWORD;
3213: foobar return TOK_KEYWORD;
3214:
3215: [a-z]+ return TOK_ID;
3216: .Ed
3217: .Pp
1.1 deraadt 3218: This is usually the best solution when appropriate.
1.16 jmc 3219: .Pp
1.1 deraadt 3220: Backing up messages tend to cascade.
1.16 jmc 3221: With a complicated set of rules it's not uncommon to get hundreds of messages.
3222: If one can decipher them, though,
3223: it often only takes a dozen or so rules to eliminate the backing up
3224: (though it's easy to make a mistake and have an error rule accidentally match
3225: a valid token; a possible future
3226: .Nm
1.1 deraadt 3227: feature will be to automatically add rules to eliminate backing up).
1.16 jmc 3228: .Pp
3229: It's important to keep in mind that the benefits of eliminating
3230: backing up are gained only if
3231: .Em every
3232: instance of backing up is eliminated.
3233: Leaving just one gains nothing.
3234: .Pp
3235: .Em Variable
3236: trailing context
3237: (where both the leading and trailing parts do not have a fixed length)
3238: entails almost the same performance loss as
3239: .Em REJECT
3240: .Pq i.e., substantial .
3241: So when possible a rule like:
3242: .Bd -literal -offset indent
3243: %%
3244: mouse|rat/(cat|dog) run();
3245: .Ed
3246: .Pp
1.1 deraadt 3247: is better written:
1.16 jmc 3248: .Bd -literal -offset indent
3249: %%
3250: mouse/cat|dog run();
3251: rat/cat|dog run();
3252: .Ed
3253: .Pp
1.1 deraadt 3254: or as
1.16 jmc 3255: .Bd -literal -offset indent
3256: %%
3257: mouse|rat/cat run();
3258: mouse|rat/dog run();
3259: .Ed
3260: .Pp
3261: Note that here the special
3262: .Sq |\&
3263: action does not provide any savings, and can even make things worse (see
3264: .Sx BUGS
3265: below).
3266: .Pp
1.1 deraadt 3267: Another area where the user can increase a scanner's performance
1.16 jmc 3268: .Pq and one that's easier to implement
3269: arises from the fact that the longer the tokens matched,
3270: the faster the scanner will run.
1.1 deraadt 3271: This is because with long tokens the processing of most input
1.16 jmc 3272: characters takes place in the
3273: .Pq short
3274: inner scanning loop, and does not often have to go through the additional work
3275: of setting up the scanning environment (e.g.,
3276: .Fa yytext )
3277: for the action.
3278: Recall the scanner for C comments:
3279: .Bd -literal -offset indent
3280: %x comment
3281: %%
3282: int line_num = 1;
3283:
3284: "/*" BEGIN(comment);
3285:
3286: <comment>[^*\en]*
3287: <comment>"*"+[^*/\en]*
3288: <comment>\en ++line_num;
3289: <comment>"*"+"/" BEGIN(INITIAL);
3290: .Ed
3291: .Pp
1.1 deraadt 3292: This could be sped up by writing it as:
1.16 jmc 3293: .Bd -literal -offset indent
3294: %x comment
3295: %%
3296: int line_num = 1;
3297:
3298: "/*" BEGIN(comment);
3299:
3300: <comment>[^*\en]*
3301: <comment>[^*\en]*\en ++line_num;
3302: <comment>"*"+[^*/\en]*
3303: <comment>"*"+[^*/\en]*\en ++line_num;
3304: <comment>"*"+"/" BEGIN(INITIAL);
3305: .Ed
3306: .Pp
3307: Now instead of each newline requiring the processing of another action,
3308: recognizing the newlines is
3309: .Qq distributed
3310: over the other rules to keep the matched text as long as possible.
3311: Note that adding rules does
3312: .Em not
3313: slow down the scanner!
3314: The speed of the scanner is independent of the number of rules or
3315: (modulo the considerations given at the beginning of this section)
3316: how complicated the rules are with regard to operators such as
3317: .Sq *
3318: and
3319: .Sq |\& .
3320: .Pp
3321: A final example in speeding up a scanner:
3322: scan through a file containing identifiers and keywords, one per line
3323: and with no other extraneous characters, and recognize all the keywords.
3324: A natural first approach is:
3325: .Bd -literal -offset indent
3326: %%
3327: asm |
3328: auto |
3329: break |
3330: \&... etc ...
3331: volatile |
3332: while /* it's a keyword */
3333:
3334: \&.|\en /* it's not a keyword */
3335: .Ed
3336: .Pp
1.1 deraadt 3337: To eliminate the back-tracking, introduce a catch-all rule:
1.16 jmc 3338: .Bd -literal -offset indent
3339: %%
3340: asm |
3341: auto |
3342: break |
3343: \&... etc ...
3344: volatile |
3345: while /* it's a keyword */
3346:
3347: [a-z]+ |
3348: \&.|\en /* it's not a keyword */
3349: .Ed
3350: .Pp
1.1 deraadt 3351: Now, if it's guaranteed that there's exactly one word per line,
3352: then we can reduce the total number of matches by a half by
1.16 jmc 3353: merging in the recognition of newlines with that of the other tokens:
3354: .Bd -literal -offset indent
3355: %%
3356: asm\en |
3357: auto\en |
3358: break\en |
3359: \&... etc ...
3360: volatile\en |
3361: while\en /* it's a keyword */
3362:
3363: [a-z]+\en |
3364: \&.|\en /* it's not a keyword */
3365: .Ed
3366: .Pp
3367: One has to be careful here,
3368: as we have now reintroduced backing up into the scanner.
3369: In particular, while we know that there will never be any characters
3370: in the input stream other than letters or newlines,
3371: .Nm
1.1 deraadt 3372: can't figure this out, and it will plan for possibly needing to back up
1.16 jmc 3373: when it has scanned a token like
3374: .Qq auto
3375: and then the next character is something other than a newline or a letter.
3376: Previously it would then just match the
3377: .Qq auto
3378: rule and be done, but now it has no
3379: .Qq auto
3380: rule, only an
3381: .Qq auto\en
3382: rule.
3383: To eliminate the possibility of backing up,
1.1 deraadt 3384: we could either duplicate all rules but without final newlines, or,
3385: since we never expect to encounter such an input and therefore don't
1.16 jmc 3386: how it's classified, we can introduce one more catch-all rule,
3387: this one which doesn't include a newline:
3388: .Bd -literal -offset indent
3389: %%
3390: asm\en |
3391: auto\en |
3392: break\en |
3393: \&... etc ...
3394: volatile\en |
3395: while\en /* it's a keyword */
3396:
3397: [a-z]+\en |
3398: [a-z]+ |
3399: \&.|\en /* it's not a keyword */
3400: .Ed
3401: .Pp
1.1 deraadt 3402: Compiled with
1.16 jmc 3403: .Fl Cf ,
1.1 deraadt 3404: this is about as fast as one can get a
1.16 jmc 3405: .Nm
1.1 deraadt 3406: scanner to go for this particular problem.
1.16 jmc 3407: .Pp
1.1 deraadt 3408: A final note:
1.16 jmc 3409: .Nm
3410: is slow when matching NUL's,
3411: particularly when a token contains multiple NUL's.
3412: It's best to write rules which match short
1.1 deraadt 3413: amounts of text if it's anticipated that the text will often include NUL's.
1.16 jmc 3414: .Pp
1.1 deraadt 3415: Another final note regarding performance: as mentioned above in the section
1.16 jmc 3416: .Sx HOW THE INPUT IS MATCHED ,
3417: dynamically resizing
3418: .Fa yytext
1.1 deraadt 3419: to accommodate huge tokens is a slow process because it presently requires that
1.16 jmc 3420: the
3421: .Pq huge
3422: token be rescanned from the beginning.
3423: Thus if performance is vital, it is better to attempt to match
3424: .Qq large
3425: quantities of text but not
3426: .Qq huge
3427: quantities, where the cutoff between the two is at about 8K characters/token.
3428: .Sh GENERATING C++ SCANNERS
3429: .Nm
3430: provides two different ways to generate scanners for use with C++.
3431: The first way is to simply compile a scanner generated by
3432: .Nm
3433: using a C++ compiler instead of a C compiler.
3434: This should not generate any compilation errors
3435: (please report any found to the email address given in the
3436: .Sx AUTHORS
3437: section below).
3438: C++ code can then be used in rule actions instead of C code.
3439: Note that the default input source for scanners remains
3440: .Fa yyin ,
1.1 deraadt 3441: and default echoing is still done to
1.16 jmc 3442: .Fa yyout .
1.1 deraadt 3443: Both of these remain
1.16 jmc 3444: .Fa FILE *
3445: variables and not C++ streams.
3446: .Pp
3447: .Nm
3448: can also be used to generate a C++ scanner class, using the
3449: .Fl +
1.1 deraadt 3450: option (or, equivalently,
1.16 jmc 3451: .Dq %option c++ ) ,
3452: which is automatically specified if the name of the flex executable ends in a
3453: .Sq + ,
3454: such as
3455: .Nm flex++ .
3456: When using this option,
3457: .Nm
3458: defaults to generating the scanner to the file
3459: .Pa lex.yy.cc
1.1 deraadt 3460: instead of
1.16 jmc 3461: .Pa lex.yy.c .
1.1 deraadt 3462: The generated scanner includes the header file
1.38 ! bentley 3463: .In g++/FlexLexer.h ,
1.1 deraadt 3464: which defines the interface to two C++ classes.
1.16 jmc 3465: .Pp
1.1 deraadt 3466: The first class,
1.16 jmc 3467: .Em FlexLexer ,
3468: provides an abstract base class defining the general scanner class interface.
3469: It provides the following member functions:
3470: .Bl -tag -width Ds
3471: .It const char* YYText()
3472: Returns the text of the most recently matched token, the equivalent of
3473: .Fa yytext .
3474: .It int YYLeng()
3475: Returns the length of the most recently matched token, the equivalent of
3476: .Fa yyleng .
3477: .It int lineno() const
3478: Returns the current input line number
1.1 deraadt 3479: (see
1.16 jmc 3480: .Dq %option yylineno ) ,
3481: or 1 if
3482: .Dq %option yylineno
1.1 deraadt 3483: was not used.
1.16 jmc 3484: .It void set_debug(int flag)
3485: Sets the debugging flag for the scanner, equivalent to assigning to
3486: .Fa yy_flex_debug
3487: (see the
3488: .Sx OPTIONS
3489: section above).
3490: Note that the scanner must be built using
3491: .Dq %option debug
1.1 deraadt 3492: to include debugging information in it.
1.16 jmc 3493: .It int debug() const
3494: Returns the current setting of the debugging flag.
3495: .El
3496: .Pp
1.1 deraadt 3497: Also provided are member functions equivalent to
1.16 jmc 3498: .Fn yy_switch_to_buffer ,
3499: .Fn yy_create_buffer
1.1 deraadt 3500: (though the first argument is an
1.18 espie 3501: .Fa std::istream*
1.1 deraadt 3502: object pointer and not a
1.16 jmc 3503: .Fa FILE* ) ,
3504: .Fn yy_flush_buffer ,
3505: .Fn yy_delete_buffer ,
1.1 deraadt 3506: and
1.16 jmc 3507: .Fn yyrestart
1.10 deraadt 3508: (again, the first argument is an
1.18 espie 3509: .Fa std::istream*
1.1 deraadt 3510: object pointer).
1.16 jmc 3511: .Pp
1.1 deraadt 3512: The second class defined in
1.38 ! bentley 3513: .In g++/FlexLexer.h
1.1 deraadt 3514: is
1.16 jmc 3515: .Fa yyFlexLexer ,
1.1 deraadt 3516: which is derived from
1.16 jmc 3517: .Fa FlexLexer .
1.1 deraadt 3518: It defines the following additional member functions:
1.16 jmc 3519: .Bl -tag -width Ds
1.18 espie 3520: .It "yyFlexLexer(std::istream* arg_yyin = 0, std::ostream* arg_yyout = 0)"
1.16 jmc 3521: Constructs a
3522: .Fa yyFlexLexer
3523: object using the given streams for input and output.
3524: If not specified, the streams default to
3525: .Fa cin
1.1 deraadt 3526: and
1.16 jmc 3527: .Fa cout ,
1.1 deraadt 3528: respectively.
1.16 jmc 3529: .It virtual int yylex()
3530: Performs the same role as
3531: .Fn yylex
1.1 deraadt 3532: does for ordinary flex scanners: it scans the input stream, consuming
1.16 jmc 3533: tokens, until a rule's action returns a value.
3534: If subclass
3535: .Sq S
3536: is derived from
3537: .Fa yyFlexLexer ,
3538: in order to access the member functions and variables of
3539: .Sq S
1.1 deraadt 3540: inside
1.16 jmc 3541: .Fn yylex ,
3542: use
3543: .Dq %option yyclass="S"
1.1 deraadt 3544: to inform
1.16 jmc 3545: .Nm
3546: that the
3547: .Sq S
3548: subclass will be used instead of
3549: .Fa yyFlexLexer .
1.1 deraadt 3550: In this case, rather than generating
1.16 jmc 3551: .Dq yyFlexLexer::yylex() ,
3552: .Nm
1.1 deraadt 3553: generates
1.16 jmc 3554: .Dq S::yylex()
1.1 deraadt 3555: (and also generates a dummy
1.16 jmc 3556: .Dq yyFlexLexer::yylex()
1.1 deraadt 3557: that calls
1.16 jmc 3558: .Dq yyFlexLexer::LexerError()
1.1 deraadt 3559: if called).
1.18 espie 3560: .It "virtual void switch_streams(std::istream* new_in = 0, std::ostream* new_out = 0)"
1.16 jmc 3561: Reassigns
3562: .Fa yyin
1.1 deraadt 3563: to
1.16 jmc 3564: .Fa new_in
3565: .Pq if non-nil
1.1 deraadt 3566: and
1.16 jmc 3567: .Fa yyout
1.1 deraadt 3568: to
1.16 jmc 3569: .Fa new_out
3570: .Pq ditto ,
3571: deleting the previous input buffer if
3572: .Fa yyin
1.1 deraadt 3573: is reassigned.
1.18 espie 3574: .It int yylex(std::istream* new_in, std::ostream* new_out = 0)
1.16 jmc 3575: First switches the input streams via
3576: .Dq switch_streams(new_in, new_out)
1.1 deraadt 3577: and then returns the value of
1.16 jmc 3578: .Fn yylex .
3579: .El
3580: .Pp
1.1 deraadt 3581: In addition,
1.16 jmc 3582: .Fa yyFlexLexer
3583: defines the following protected virtual functions which can be redefined
1.1 deraadt 3584: in derived classes to tailor the scanner:
1.16 jmc 3585: .Bl -tag -width Ds
3586: .It virtual int LexerInput(char* buf, int max_size)
3587: Reads up to
3588: .Fa max_size
1.1 deraadt 3589: characters into
1.16 jmc 3590: .Fa buf
3591: and returns the number of characters read.
3592: To indicate end-of-input, return 0 characters.
3593: Note that
3594: .Qq interactive
3595: scanners (see the
3596: .Fl B
1.1 deraadt 3597: and
1.16 jmc 3598: .Fl I
1.1 deraadt 3599: flags) define the macro
1.16 jmc 3600: .Dv YY_INTERACTIVE .
3601: If
3602: .Fn LexerInput
3603: has been redefined, and it's necessary to take different actions depending on
3604: whether or not the scanner might be scanning an interactive input source,
3605: it's possible to test for the presence of this name via
3606: .Dq #ifdef .
3607: .It virtual void LexerOutput(const char* buf, int size)
3608: Writes out
3609: .Fa size
1.1 deraadt 3610: characters from the buffer
1.16 jmc 3611: .Fa buf ,
3612: which, while NUL-terminated, may also contain
3613: .Qq internal
3614: NUL's if the scanner's rules can match text with NUL's in them.
3615: .It virtual void LexerError(const char* msg)
3616: Reports a fatal error message.
3617: The default version of this function writes the message to the stream
3618: .Fa cerr
1.1 deraadt 3619: and exits.
1.16 jmc 3620: .El
3621: .Pp
1.1 deraadt 3622: Note that a
1.16 jmc 3623: .Fa yyFlexLexer
3624: object contains its entire scanning state.
3625: Thus such objects can be used to create reentrant scanners.
3626: Multiple instances of the same
3627: .Fa yyFlexLexer
3628: class can be instantiated, and multiple C++ scanner classes can be combined
1.1 deraadt 3629: in the same program using the
1.16 jmc 3630: .Fl P
1.1 deraadt 3631: option discussed above.
1.16 jmc 3632: .Pp
1.1 deraadt 3633: Finally, note that the
1.16 jmc 3634: .Dq %array
3635: feature is not available to C++ scanner classes;
3636: .Dq %pointer
3637: must be used
3638: .Pq the default .
3639: .Pp
1.1 deraadt 3640: Here is an example of a simple C++ scanner:
1.16 jmc 3641: .Bd -literal -offset indent
3642: // An example of using the flex C++ scanner class.
1.1 deraadt 3643:
1.16 jmc 3644: %{
3645: #include <errno.h>
3646: int mylineno = 0;
3647: %}
1.1 deraadt 3648:
1.16 jmc 3649: string \e"[^\en"]+\e"
1.1 deraadt 3650:
1.16 jmc 3651: ws [ \et]+
1.1 deraadt 3652:
1.16 jmc 3653: alpha [A-Za-z]
3654: dig [0-9]
3655: name ({alpha}|{dig}|\e$)({alpha}|{dig}|[_.\e-/$])*
3656: num1 [-+]?{dig}+\e.?([eE][-+]?{dig}+)?
3657: num2 [-+]?{dig}*\e.{dig}+([eE][-+]?{dig}+)?
3658: number {num1}|{num2}
1.1 deraadt 3659:
1.16 jmc 3660: %%
1.1 deraadt 3661:
1.16 jmc 3662: {ws} /* skip blanks and tabs */
1.1 deraadt 3663:
1.16 jmc 3664: "/*" {
3665: int c;
1.1 deraadt 3666:
1.16 jmc 3667: while ((c = yyinput()) != 0) {
3668: if(c == '\en')
1.1 deraadt 3669: ++mylineno;
1.16 jmc 3670: else if(c == '*') {
3671: if ((c = yyinput()) == '/')
1.1 deraadt 3672: break;
3673: else
3674: unput(c);
3675: }
1.16 jmc 3676: }
3677: }
1.1 deraadt 3678:
1.16 jmc 3679: {number} cout << "number " << YYText() << '\en';
1.1 deraadt 3680:
1.16 jmc 3681: \en mylineno++;
1.1 deraadt 3682:
1.16 jmc 3683: {name} cout << "name " << YYText() << '\en';
1.1 deraadt 3684:
1.16 jmc 3685: {string} cout << "string " << YYText() << '\en';
3686:
3687: %%
3688:
3689: int main(int /* argc */, char** /* argv */)
3690: {
3691: FlexLexer* lexer = new yyFlexLexer;
3692: while(lexer->yylex() != 0)
3693: ;
3694: return 0;
3695: }
3696: .Ed
3697: .Pp
3698: To create multiple
3699: .Pq different
3700: lexer classes, use the
3701: .Fl P
3702: flag
3703: (or the
3704: .Dq prefix=
3705: option)
3706: to rename each
3707: .Fa yyFlexLexer
1.1 deraadt 3708: to some other
1.16 jmc 3709: .Fa xxFlexLexer .
1.38 ! bentley 3710: .In g++/FlexLexer.h
1.16 jmc 3711: can then be included in other sources once per lexer class, first renaming
3712: .Fa yyFlexLexer
1.1 deraadt 3713: as follows:
1.16 jmc 3714: .Bd -literal -offset indent
3715: #undef yyFlexLexer
3716: #define yyFlexLexer xxFlexLexer
3717: #include <g++/FlexLexer.h>
3718:
3719: #undef yyFlexLexer
3720: #define yyFlexLexer zzFlexLexer
3721: #include <g++/FlexLexer.h>
3722: .Ed
3723: .Pp
3724: If, for example,
3725: .Dq %option prefix="xx"
3726: is used for one scanner and
3727: .Dq %option prefix="zz"
3728: is used for the other.
3729: .Pp
3730: .Sy IMPORTANT :
3731: the present form of the scanning class is experimental
1.7 aaron 3732: and may change considerably between major releases.
1.16 jmc 3733: .Sh INCOMPATIBILITIES WITH LEX AND POSIX
3734: .Nm
1.25 sobrado 3735: is a rewrite of the
3736: .At
1.16 jmc 3737: .Nm lex
3738: tool
3739: (the two implementations do not share any code, though),
3740: with some extensions and incompatibilities, both of which are of concern
3741: to those who wish to write scanners acceptable to either implementation.
3742: .Nm
3743: is fully compliant with the
3744: .Tn POSIX
3745: .Nm lex
1.1 deraadt 3746: specification, except that when using
1.16 jmc 3747: .Dq %pointer
3748: .Pq the default ,
3749: a call to
3750: .Fn unput
1.1 deraadt 3751: destroys the contents of
1.16 jmc 3752: .Fa yytext ,
3753: which is counter to the
3754: .Tn POSIX
3755: specification.
3756: .Pp
3757: In this section we discuss all of the known areas of incompatibility between
3758: .Nm ,
1.36 schwarze 3759: .At
1.16 jmc 3760: .Nm lex ,
3761: and the
3762: .Tn POSIX
3763: specification.
3764: .Pp
3765: .Nm flex Ns 's
3766: .Fl l
1.36 schwarze 3767: option turns on maximum compatibility with the original
3768: .At
1.16 jmc 3769: .Nm lex
1.1 deraadt 3770: implementation, at the cost of a major loss in the generated scanner's
1.16 jmc 3771: performance.
3772: We note below which incompatibilities can be overcome using the
3773: .Fl l
1.1 deraadt 3774: option.
1.16 jmc 3775: .Pp
3776: .Nm
1.1 deraadt 3777: is fully compatible with
1.16 jmc 3778: .Nm lex
1.1 deraadt 3779: with the following exceptions:
1.16 jmc 3780: .Bl -dash
3781: .It
1.1 deraadt 3782: The undocumented
1.16 jmc 3783: .Nm lex
1.1 deraadt 3784: scanner internal variable
1.16 jmc 3785: .Fa yylineno
1.1 deraadt 3786: is not supported unless
1.16 jmc 3787: .Fl l
1.1 deraadt 3788: or
1.16 jmc 3789: .Dq %option yylineno
1.1 deraadt 3790: is used.
1.16 jmc 3791: .Pp
3792: .Fa yylineno
1.1 deraadt 3793: should be maintained on a per-buffer basis, rather than a per-scanner
1.16 jmc 3794: .Pq single global variable
3795: basis.
3796: .Pp
3797: .Fa yylineno
3798: is not part of the
3799: .Tn POSIX
3800: specification.
3801: .It
1.1 deraadt 3802: The
1.16 jmc 3803: .Fn input
1.1 deraadt 3804: routine is not redefinable, though it may be called to read characters
1.16 jmc 3805: following whatever has been matched by a rule.
3806: If
3807: .Fn input
3808: encounters an end-of-file, the normal
3809: .Fn yywrap
3810: processing is done.
3811: A
3812: .Dq real
3813: end-of-file is returned by
3814: .Fn input
1.1 deraadt 3815: as
1.16 jmc 3816: .Dv EOF .
3817: .Pp
1.1 deraadt 3818: Input is instead controlled by defining the
1.16 jmc 3819: .Dv YY_INPUT
1.1 deraadt 3820: macro.
1.16 jmc 3821: .Pp
1.1 deraadt 3822: The
1.16 jmc 3823: .Nm
1.1 deraadt 3824: restriction that
1.16 jmc 3825: .Fn input
3826: cannot be redefined is in accordance with the
3827: .Tn POSIX
3828: specification, which simply does not specify any way of controlling the
1.1 deraadt 3829: scanner's input other than by making an initial assignment to
1.16 jmc 3830: .Fa yyin .
3831: .It
1.1 deraadt 3832: The
1.16 jmc 3833: .Fn unput
3834: routine is not redefinable.
3835: This restriction is in accordance with
3836: .Tn POSIX .
3837: .It
3838: .Nm
1.1 deraadt 3839: scanners are not as reentrant as
1.16 jmc 3840: .Nm lex
3841: scanners.
3842: In particular, if a scanner is interactive and
3843: an interrupt handler long-jumps out of the scanner,
3844: and the scanner is subsequently called again,
3845: the following error message may be displayed:
3846: .Pp
3847: .D1 fatal flex scanner internal error--end of buffer missed
3848: .Pp
1.1 deraadt 3849: To reenter the scanner, first use
1.16 jmc 3850: .Pp
3851: .Dl yyrestart(yyin);
3852: .Pp
3853: Note that this call will throw away any buffered input;
3854: usually this isn't a problem with an interactive scanner.
3855: .Pp
3856: Also note that flex C++ scanner classes are reentrant,
3857: so if using C++ is an option , they should be used instead.
3858: See
3859: .Sx GENERATING C++ SCANNERS
3860: above for details.
3861: .It
3862: .Fn output
1.1 deraadt 3863: is not supported.
3864: Output from the
1.16 jmc 3865: .Em ECHO
1.1 deraadt 3866: macro is done to the file-pointer
1.16 jmc 3867: .Fa yyout
3868: .Pq default stdout .
3869: .Pp
3870: .Fn output
3871: is not part of the
3872: .Tn POSIX
3873: specification.
3874: .It
3875: .Nm lex
3876: does not support exclusive start conditions
3877: .Pq %x ,
3878: though they are in the
3879: .Tn POSIX
3880: specification.
3881: .It
1.1 deraadt 3882: When definitions are expanded,
1.16 jmc 3883: .Nm
1.1 deraadt 3884: encloses them in parentheses.
1.16 jmc 3885: With
3886: .Nm lex ,
3887: the following:
3888: .Bd -literal -offset indent
3889: NAME [A-Z][A-Z0-9]*
3890: %%
3891: foo{NAME}? printf("Found it\en");
3892: %%
3893: .Ed
3894: .Pp
3895: will not match the string
3896: .Qq foo
3897: because when the macro is expanded the rule is equivalent to
3898: .Qq foo[A-Z][A-Z0-9]*?
3899: and the precedence is such that the
3900: .Sq ?\&
3901: is associated with
3902: .Qq [A-Z0-9]* .
3903: With
3904: .Nm ,
1.1 deraadt 3905: the rule will be expanded to
1.16 jmc 3906: .Qq foo([A-Z][A-Z0-9]*)?
3907: and so the string
3908: .Qq foo
3909: will match.
3910: .Pp
1.1 deraadt 3911: Note that if the definition begins with
1.16 jmc 3912: .Sq ^
1.1 deraadt 3913: or ends with
1.16 jmc 3914: .Sq $
3915: then it is not expanded with parentheses, to allow these operators to appear in
3916: definitions without losing their special meanings.
3917: But the
3918: .Sq Aq s ,
3919: .Sq / ,
1.1 deraadt 3920: and
1.16 jmc 3921: .Aq Aq EOF
1.1 deraadt 3922: operators cannot be used in a
1.16 jmc 3923: .Nm
1.1 deraadt 3924: definition.
1.16 jmc 3925: .Pp
1.1 deraadt 3926: Using
1.16 jmc 3927: .Fl l
1.1 deraadt 3928: results in the
1.16 jmc 3929: .Nm lex
1.1 deraadt 3930: behavior of no parentheses around the definition.
1.16 jmc 3931: .Pp
3932: The
3933: .Tn POSIX
3934: specification is that the definition be enclosed in parentheses.
3935: .It
1.1 deraadt 3936: Some implementations of
1.16 jmc 3937: .Nm lex
3938: allow a rule's action to begin on a separate line,
3939: if the rule's pattern has trailing whitespace:
3940: .Bd -literal -offset indent
3941: %%
3942: foo|bar<space here>
3943: { foobar_action(); }
3944: .Ed
3945: .Pp
3946: .Nm
1.1 deraadt 3947: does not support this feature.
1.16 jmc 3948: .It
1.1 deraadt 3949: The
1.16 jmc 3950: .Nm lex
3951: .Sq %r
3952: .Pq generate a Ratfor scanner
3953: option is not supported.
3954: It is not part of the
3955: .Tn POSIX
3956: specification.
3957: .It
1.1 deraadt 3958: After a call to
1.16 jmc 3959: .Fn unput ,
3960: .Fa yytext
3961: is undefined until the next token is matched,
3962: unless the scanner was built using
3963: .Dq %array .
1.1 deraadt 3964: This is not the case with
1.16 jmc 3965: .Nm lex
3966: or the
3967: .Tn POSIX
3968: specification.
3969: The
3970: .Fl l
1.1 deraadt 3971: option does away with this incompatibility.
1.16 jmc 3972: .It
1.1 deraadt 3973: The precedence of the
1.16 jmc 3974: .Sq {}
3975: .Pq numeric range
3976: operator is different.
3977: .Nm lex
3978: interprets
3979: .Qq abc{1,3}
3980: as match one, two, or three occurrences of
3981: .Sq abc ,
3982: whereas
3983: .Nm
3984: interprets it as match
3985: .Sq ab
3986: followed by one, two, or three occurrences of
3987: .Sq c .
3988: The latter is in agreement with the
3989: .Tn POSIX
3990: specification.
3991: .It
1.1 deraadt 3992: The precedence of the
1.16 jmc 3993: .Sq ^
1.1 deraadt 3994: operator is different.
1.16 jmc 3995: .Nm lex
3996: interprets
3997: .Qq ^foo|bar
3998: as match either
3999: .Sq foo
4000: at the beginning of a line, or
4001: .Sq bar
4002: anywhere, whereas
4003: .Nm
4004: interprets it as match either
4005: .Sq foo
4006: or
4007: .Sq bar
4008: if they come at the beginning of a line.
4009: The latter is in agreement with the
4010: .Tn POSIX
4011: specification.
4012: .It
1.1 deraadt 4013: The special table-size declarations such as
1.16 jmc 4014: .Sq %a
1.1 deraadt 4015: supported by
1.16 jmc 4016: .Nm lex
1.1 deraadt 4017: are not required by
1.16 jmc 4018: .Nm
1.1 deraadt 4019: scanners;
1.16 jmc 4020: .Nm
1.1 deraadt 4021: ignores them.
1.16 jmc 4022: .It
1.1 deraadt 4023: The name
1.16 jmc 4024: .Dv FLEX_SCANNER
1.1 deraadt 4025: is #define'd so scanners may be written for use with either
1.16 jmc 4026: .Nm
1.1 deraadt 4027: or
1.16 jmc 4028: .Nm lex .
1.1 deraadt 4029: Scanners also include
1.16 jmc 4030: .Dv YY_FLEX_MAJOR_VERSION
1.1 deraadt 4031: and
1.16 jmc 4032: .Dv YY_FLEX_MINOR_VERSION
1.1 deraadt 4033: indicating which version of
1.16 jmc 4034: .Nm
1.1 deraadt 4035: generated the scanner
1.16 jmc 4036: (for example, for the 2.5 release, these defines would be 2 and 5,
1.1 deraadt 4037: respectively).
1.16 jmc 4038: .El
4039: .Pp
1.1 deraadt 4040: The following
1.16 jmc 4041: .Nm
1.1 deraadt 4042: features are not included in
1.16 jmc 4043: .Nm lex
4044: or the
4045: .Tn POSIX
4046: specification:
4047: .Bd -unfilled -offset indent
4048: C++ scanners
4049: %option
4050: start condition scopes
4051: start condition stacks
4052: interactive/non-interactive scanners
4053: yy_scan_string() and friends
4054: yyterminate()
4055: yy_set_interactive()
4056: yy_set_bol()
4057: YY_AT_BOL()
4058: <<EOF>>
4059: <*>
4060: YY_DECL
4061: YY_START
4062: YY_USER_ACTION
4063: YY_USER_INIT
4064: #line directives
4065: %{}'s around actions
4066: multiple actions on a line
4067: .Ed
4068: .Pp
4069: plus almost all of the
4070: .Nm
4071: flags.
1.1 deraadt 4072: The last feature in the list refers to the fact that with
1.16 jmc 4073: .Nm
1.37 jmc 4074: multiple actions can be placed on the same line,
1.16 jmc 4075: separated with semi-colons, while with
4076: .Nm lex ,
1.1 deraadt 4077: the following
1.16 jmc 4078: .Pp
4079: .Dl foo handle_foo(); ++num_foos_seen;
4080: .Pp
4081: is
4082: .Pq rather surprisingly
4083: truncated to
4084: .Pp
4085: .Dl foo handle_foo();
4086: .Pp
4087: .Nm
4088: does not truncate the action.
4089: Actions that are not enclosed in braces
4090: are simply terminated at the end of the line.
4091: .Sh FILES
4092: .Bl -tag -width "<g++/FlexLexer.h>"
4093: .It flex.skl
4094: Skeleton scanner.
4095: This file is only used when building flex, not when
4096: .Nm
4097: executes.
4098: .It lex.backup
4099: Backing-up information for the
4100: .Fl b
4101: flag (called
4102: .Pa lex.bck
4103: on some systems).
4104: .It lex.yy.c
4105: Generated scanner
4106: (called
4107: .Pa lexyy.c
4108: on some systems).
4109: .It lex.yy.cc
4110: Generated C++ scanner class, when using
4111: .Fl + .
1.38 ! bentley 4112: .It In g++/FlexLexer.h
1.16 jmc 4113: Header file defining the C++ scanner base class,
4114: .Fa FlexLexer ,
4115: and its derived class,
4116: .Fa yyFlexLexer .
4117: .It /usr/lib/libl.*
4118: .Nm
4119: libraries.
4120: The
4121: .Pa /usr/lib/libfl.*\&
4122: libraries are links to these.
4123: Scanners must be linked using either
4124: .Fl \&ll
4125: or
4126: .Fl lfl .
4127: .El
1.29 jmc 4128: .Sh EXIT STATUS
4129: .Ex -std flex
1.16 jmc 4130: .Sh DIAGNOSTICS
4131: .Bl -diag
4132: .It warning, rule cannot be matched
4133: Indicates that the given rule cannot be matched because it follows other rules
4134: that will always match the same text as it.
4135: For example, in the following
4136: .Dq foo
4137: cannot be matched because it comes after an identifier
4138: .Qq catch-all
4139: rule:
4140: .Bd -literal -offset indent
4141: [a-z]+ got_identifier();
4142: foo got_foo();
4143: .Ed
4144: .Pp
1.1 deraadt 4145: Using
1.16 jmc 4146: .Em REJECT
1.1 deraadt 4147: in a scanner suppresses this warning.
1.16 jmc 4148: .It "warning, \-s option given but default rule can be matched"
4149: Means that it is possible
4150: .Pq perhaps only in a particular start condition
4151: that the default rule
4152: .Pq match any single character
4153: is the only one that will match a particular input.
4154: Since
4155: .Fl s
1.1 deraadt 4156: was given, presumably this is not intended.
1.16 jmc 4157: .It reject_used_but_not_detected undefined
4158: .It yymore_used_but_not_detected undefined
4159: These errors can occur at compile time.
4160: They indicate that the scanner uses
4161: .Em REJECT
1.1 deraadt 4162: or
1.16 jmc 4163: .Fn yymore
1.1 deraadt 4164: but that
1.16 jmc 4165: .Nm
1.1 deraadt 4166: failed to notice the fact, meaning that
1.16 jmc 4167: .Nm
1.1 deraadt 4168: scanned the first two sections looking for occurrences of these actions
1.16 jmc 4169: and failed to find any, but somehow they snuck in
4170: .Pq via an #include file, for example .
4171: Use
4172: .Dq %option reject
4173: or
4174: .Dq %option yymore
4175: to indicate to
4176: .Nm
4177: that these features are really needed.
4178: .It flex scanner jammed
4179: A scanner compiled with
4180: .Fl s
4181: has encountered an input string which wasn't matched by any of its rules.
4182: This error can also occur due to internal problems.
4183: .It token too large, exceeds YYLMAX
4184: The scanner uses
4185: .Dq %array
1.1 deraadt 4186: and one of its rules matched a string longer than the
1.16 jmc 4187: .Dv YYLMAX
4188: constant
4189: .Pq 8K bytes by default .
4190: The value can be increased by #define'ing
4191: .Dv YYLMAX
4192: in the definitions section of
4193: .Nm
1.1 deraadt 4194: input.
1.16 jmc 4195: .It "scanner requires \-8 flag to use the character 'x'"
4196: The scanner specification includes recognizing the 8-bit character
4197: .Sq x
4198: and the
4199: .Fl 8
4200: flag was not specified, and defaulted to 7-bit because the
4201: .Fl Cf
4202: or
4203: .Fl CF
4204: table compression options were used.
4205: See the discussion of the
4206: .Fl 7
1.1 deraadt 4207: flag for details.
1.16 jmc 4208: .It flex scanner push-back overflow
4209: unput() was used to push back so much text that the scanner's buffer
4210: could not hold both the pushed-back text and the current token in
4211: .Fa yytext .
4212: Ideally the scanner should dynamically resize the buffer in this case,
4213: but at present it does not.
4214: .It "input buffer overflow, can't enlarge buffer because scanner uses REJECT"
4215: The scanner was working on matching an extremely large token and needed
4216: to expand the input buffer.
4217: This doesn't work with scanners that use
4218: .Em REJECT .
4219: .It "fatal flex scanner internal error--end of buffer missed"
1.1 deraadt 4220: This can occur in an scanner which is reentered after a long-jump
1.16 jmc 4221: has jumped out
4222: .Pq or over
4223: the scanner's activation frame.
4224: Before reentering the scanner, use:
4225: .Pp
4226: .Dl yyrestart(yyin);
4227: .Pp
1.1 deraadt 4228: or, as noted above, switch to using the C++ scanner class.
1.16 jmc 4229: .It "too many start conditions in <> construct!"
4230: More start conditions than exist were listed in a <> construct
4231: (so at least one of them must have been listed twice).
4232: .El
4233: .Sh SEE ALSO
4234: .Xr awk 1 ,
4235: .Xr sed 1 ,
4236: .Xr yacc 1
4237: .Rs
4238: .%A John Levine
4239: .%A Tony Mason
4240: .%A Doug Brown
4241: .%B Lex & Yacc
4242: .%I O'Reilly and Associates
4243: .%N 2nd edition
4244: .Re
4245: .Rs
4246: .%A Alfred Aho
4247: .%A Ravi Sethi
4248: .%A Jeffrey Ullman
4249: .%B Compilers: Principles, Techniques and Tools
4250: .%I Addison-Wesley
4251: .%D 1986
4252: .%O "Describes the pattern-matching techniques used by flex (deterministic finite automata)"
4253: .Re
1.23 jmc 4254: .Sh STANDARDS
4255: The
4256: .Nm lex
4257: utility is compliant with the
4258: .St -p1003.1-2008
4259: specification,
4260: though its presence is optional.
4261: .Pp
4262: The flags
1.31 jmc 4263: .Op Fl 78BbCdFfhIiLloPpSsTVw+? ,
1.23 jmc 4264: .Op Fl -help ,
4265: and
4266: .Op Fl -version
4267: are extensions to that specification.
1.37 jmc 4268: .Pp
4269: See also the
4270: .Sx INCOMPATIBILITIES WITH LEX AND POSIX
4271: section, above.
1.16 jmc 4272: .Sh AUTHORS
1.1 deraadt 4273: Vern Paxson, with the help of many ideas and much inspiration from
1.16 jmc 4274: Van Jacobson.
4275: Original version by Jef Poskanzer.
4276: The fast table representation is a partial implementation of a design done by
4277: Van Jacobson.
4278: The implementation was done by Kevin Gong and Vern Paxson.
4279: .Pp
1.1 deraadt 4280: Thanks to the many
1.16 jmc 4281: .Nm
1.1 deraadt 4282: beta-testers, feedbackers, and contributors, especially Francois Pinard,
4283: Casey Leedom,
4284: Robert Abramovitz,
4285: Stan Adermann, Terry Allen, David Barker-Plummer, John Basrai,
4286: Neal Becker, Nelson H.F. Beebe, benson@odi.com,
4287: Karl Berry, Peter A. Bigot, Simon Blanchard,
4288: Keith Bostic, Frederic Brehm, Ian Brockbank, Kin Cho, Nick Christopher,
4289: Brian Clapper, J.T. Conklin,
4290: Jason Coughlin, Bill Cox, Nick Cropper, Dave Curtis, Scott David
1.11 deraadt 4291: Daniels, Chris G. Demetriou, Theo de Raadt,
1.1 deraadt 4292: Mike Donahue, Chuck Doucette, Tom Epperly, Leo Eskin,
4293: Chris Faylor, Chris Flatters, Jon Forrest, Jeffrey Friedl,
4294: Joe Gayda, Kaveh R. Ghazi, Wolfgang Glunz,
4295: Eric Goldman, Christopher M. Gould, Ulrich Grepel, Peer Griebel,
4296: Jan Hajic, Charles Hemphill, NORO Hideo,
4297: Jarkko Hietaniemi, Scott Hofmann,
4298: Jeff Honig, Dana Hudes, Eric Hughes, John Interrante,
4299: Ceriel Jacobs, Michal Jaegermann, Sakari Jalovaara, Jeffrey R. Jones,
4300: Henry Juengst, Klaus Kaempf, Jonathan I. Kamens, Terrence O Kane,
4301: Amir Katz, ken@ken.hilco.com, Kevin B. Kenny,
4302: Steve Kirsch, Winfried Koenig, Marq Kole, Ronald Lamprecht,
4303: Greg Lee, Rohan Lenard, Craig Leres, John Levine, Steve Liddle,
4304: David Loffredo, Mike Long,
4305: Mohamed el Lozy, Brian Madsen, Malte, Joe Marshall,
4306: Bengt Martensson, Chris Metcalf,
4307: Luke Mewburn, Jim Meyering, R. Alexander Milowski, Erik Naggum,
4308: G.T. Nicol, Landon Noll, James Nordby, Marc Nozell,
4309: Richard Ohnemus, Karsten Pahnke,
1.16 jmc 4310: Sven Panne, Roland Pesch, Walter Pelissero, Gaumond Pierre,
4311: Esmond Pitt, Jef Poskanzer, Joe Rahmeh, Jarmo Raiha,
1.1 deraadt 4312: Frederic Raimbault, Pat Rankin, Rick Richardson,
4313: Kevin Rodgers, Kai Uwe Rommel, Jim Roskind, Alberto Santini,
4314: Andreas Scherer, Darrell Schiebel, Raf Schietekat,
4315: Doug Schmidt, Philippe Schnoebelen, Andreas Schwab,
4316: Larry Schwimmer, Alex Siegel, Eckehard Stolz, Jan-Erik Strvmquist,
4317: Mike Stump, Paul Stuart, Dave Tallman, Ian Lance Taylor,
4318: Chris Thewalt, Richard M. Timoney, Jodi Tsai,
1.16 jmc 4319: Paul Tuinenga, Gary Weik, Frank Whaley, Gerhard Wilhelms, Kent Williams,
4320: Ken Yap, Ron Zellar, Nathan Zelle, David Zuhn,
4321: and those whose names have slipped my marginal mail-archiving skills
4322: but whose contributions are appreciated all the
1.1 deraadt 4323: same.
1.16 jmc 4324: .Pp
1.1 deraadt 4325: Thanks to Keith Bostic, Jon Forrest, Noah Friedman,
4326: John Gilmore, Craig Leres, John Levine, Bob Mulcahy, G.T.
4327: Nicol, Francois Pinard, Rich Salz, and Richard Stallman for help with various
4328: distribution headaches.
1.16 jmc 4329: .Pp
4330: Thanks to Esmond Pitt and Earle Horton for 8-bit character support;
4331: to Benson Margulies and Fred Burke for C++ support;
4332: to Kent Williams and Tom Epperly for C++ class support;
4333: to Ove Ewerlid for support of NUL's;
4334: and to Eric Hughes for support of multiple buffers.
4335: .Pp
1.1 deraadt 4336: This work was primarily done when I was with the Real Time Systems Group
1.16 jmc 4337: at the Lawrence Berkeley Laboratory in Berkeley, CA.
4338: Many thanks to all there for the support I received.
4339: .Pp
4340: Send comments to
1.34 schwarze 4341: .Aq Mt vern@ee.lbl.gov .
1.16 jmc 4342: .Sh BUGS
4343: Some trailing context patterns cannot be properly matched and generate
4344: warning messages
4345: .Pq "dangerous trailing context" .
4346: These are patterns where the ending of the first part of the rule
4347: matches the beginning of the second part, such as
4348: .Qq zx*/xy* ,
4349: where the
4350: .Sq x*
4351: matches the
4352: .Sq x
4353: at the beginning of the trailing context.
4354: (Note that the POSIX draft states that the text matched by such patterns
4355: is undefined.)
4356: .Pp
4357: For some trailing context rules, parts which are actually fixed-length are
4358: not recognized as such, leading to the above mentioned performance loss.
4359: In particular, parts using
4360: .Sq |\&
4361: or
4362: .Sq {n}
4363: (such as
4364: .Qq foo{3} )
4365: are always considered variable-length.
4366: .Pp
4367: Combining trailing context with the special
4368: .Sq |\&
4369: action can result in fixed trailing context being turned into
4370: the more expensive variable trailing context.
4371: For example, in the following:
4372: .Bd -literal -offset indent
4373: %%
4374: abc |
4375: xyz/def
4376: .Ed
4377: .Pp
4378: Use of
4379: .Fn unput
4380: invalidates yytext and yyleng, unless the
4381: .Dq %array
4382: directive
4383: or the
4384: .Fl l
4385: option has been used.
4386: .Pp
4387: Pattern-matching of NUL's is substantially slower than matching other
4388: characters.
4389: .Pp
4390: Dynamic resizing of the input buffer is slow, as it entails rescanning
4391: all the text matched so far by the current
4392: .Pq generally huge
4393: token.
4394: .Pp
4395: Due to both buffering of input and read-ahead,
4396: it is not possible to intermix calls to
1.38 ! bentley 4397: .In stdio.h
1.16 jmc 4398: routines, such as, for example,
4399: .Fn getchar ,
4400: with
4401: .Nm
4402: rules and expect it to work.
4403: Call
4404: .Fn input
4405: instead.
4406: .Pp
4407: The total table entries listed by the
4408: .Fl v
4409: flag excludes the number of table entries needed to determine
4410: what rule has been matched.
4411: The number of entries is equal to the number of DFA states
4412: if the scanner does not use
4413: .Em REJECT ,
4414: and somewhat greater than the number of states if it does.
4415: .Pp
4416: .Em REJECT
4417: cannot be used with the
4418: .Fl f
4419: or
4420: .Fl F
4421: options.
4422: .Pp
4423: The
4424: .Nm
4425: internal algorithms need documentation.
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