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1 nigel 63 <html>
2     <head>
3     <title>pcreapi specification</title>
4     </head>
5     <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6     This HTML document has been generated automatically from the original man page.
7     If there is any nonsense in it, please consult the man page, in case the
8     conversion went wrong.<br>
9     <ul>
10     <li><a name="TOC1" href="#SEC1">SYNOPSIS OF PCRE API</a>
11     <li><a name="TOC2" href="#SEC2">PCRE API</a>
12     <li><a name="TOC3" href="#SEC3">MULTITHREADING</a>
13     <li><a name="TOC4" href="#SEC4">CHECKING BUILD-TIME OPTIONS</a>
14     <li><a name="TOC5" href="#SEC5">COMPILING A PATTERN</a>
15     <li><a name="TOC6" href="#SEC6">STUDYING A PATTERN</a>
16     <li><a name="TOC7" href="#SEC7">LOCALE SUPPORT</a>
17     <li><a name="TOC8" href="#SEC8">INFORMATION ABOUT A PATTERN</a>
18     <li><a name="TOC9" href="#SEC9">OBSOLETE INFO FUNCTION</a>
19     <li><a name="TOC10" href="#SEC10">MATCHING A PATTERN</a>
20     <li><a name="TOC11" href="#SEC11">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a>
21     <li><a name="TOC12" href="#SEC12">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a>
22     </ul>
23     <br><a name="SEC1" href="#TOC1">SYNOPSIS OF PCRE API</a><br>
24     <P>
25     <b>#include &#60;pcre.h&#62;</b>
26     </P>
27     <P>
28     <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
29     <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
30     <b>const unsigned char *<i>tableptr</i>);</b>
31     </P>
32     <P>
33     <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
34     <b>const char **<i>errptr</i>);</b>
35     </P>
36     <P>
37     <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
38     <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
39     <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
40     </P>
41     <P>
42     <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
43     <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
44     <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
45     <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
46     </P>
47     <P>
48     <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
49     <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
50     <b>int <i>buffersize</i>);</b>
51     </P>
52     <P>
53     <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
54     <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
55     <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
56     <b>const char **<i>stringptr</i>);</b>
57     </P>
58     <P>
59     <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
60     <b>const char *<i>name</i>);</b>
61     </P>
62     <P>
63     <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
64     <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
65     <b>const char **<i>stringptr</i>);</b>
66     </P>
67     <P>
68     <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
69     <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
70     </P>
71     <P>
72     <b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
73     </P>
74     <P>
75     <b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
76     </P>
77     <P>
78     <b>const unsigned char *pcre_maketables(void);</b>
79     </P>
80     <P>
81     <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
82     <b>int <i>what</i>, void *<i>where</i>);</b>
83     </P>
84     <P>
85     <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
86     <b>*<i>firstcharptr</i>);</b>
87     </P>
88     <P>
89     <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
90     </P>
91     <P>
92     <b>char *pcre_version(void);</b>
93     </P>
94     <P>
95     <b>void *(*pcre_malloc)(size_t);</b>
96     </P>
97     <P>
98     <b>void (*pcre_free)(void *);</b>
99     </P>
100     <P>
101     <b>int (*pcre_callout)(pcre_callout_block *);</b>
102     </P>
103     <br><a name="SEC2" href="#TOC1">PCRE API</a><br>
104     <P>
105     PCRE has its own native API, which is described in this document. There is also
106     a set of wrapper functions that correspond to the POSIX regular expression API.
107     These are described in the <b>pcreposix</b> documentation.
108     </P>
109     <P>
110     The native API function prototypes are defined in the header file <b>pcre.h</b>,
111     and on Unix systems the library itself is called <b>libpcre.a</b>, so can be
112     accessed by adding <b>-lpcre</b> to the command for linking an application which
113     calls it. The header file defines the macros PCRE_MAJOR and PCRE_MINOR to
114     contain the major and minor release numbers for the library. Applications can
115     use these to include support for different releases.
116     </P>
117     <P>
118     The functions <b>pcre_compile()</b>, <b>pcre_study()</b>, and <b>pcre_exec()</b>
119     are used for compiling and matching regular expressions. A sample program that
120     demonstrates the simplest way of using them is given in the file
121     <i>pcredemo.c</i>. The <b>pcresample</b> documentation describes how to run it.
122     </P>
123     <P>
124     There are convenience functions for extracting captured substrings from a
125     matched subject string. They are:
126     </P>
127     <P>
128     <pre>
129     <b>pcre_copy_substring()</b>
130     <b>pcre_copy_named_substring()</b>
131     <b>pcre_get_substring()</b>
132     <b>pcre_get_named_substring()</b>
133     <b>pcre_get_substring_list()</b>
134     </PRE>
135     </P>
136     <P>
137     <b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
138     provided, to free the memory used for extracted strings.
139     </P>
140     <P>
141     The function <b>pcre_maketables()</b> is used (optionally) to build a set of
142     character tables in the current locale for passing to <b>pcre_compile()</b>.
143     </P>
144     <P>
145     The function <b>pcre_fullinfo()</b> is used to find out information about a
146     compiled pattern; <b>pcre_info()</b> is an obsolete version which returns only
147     some of the available information, but is retained for backwards compatibility.
148     The function <b>pcre_version()</b> returns a pointer to a string containing the
149     version of PCRE and its date of release.
150     </P>
151     <P>
152     The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
153     the entry points of the standard <b>malloc()</b> and <b>free()</b> functions
154     respectively. PCRE calls the memory management functions via these variables,
155     so a calling program can replace them if it wishes to intercept the calls. This
156     should be done before calling any PCRE functions.
157     </P>
158     <P>
159     The global variable <b>pcre_callout</b> initially contains NULL. It can be set
160     by the caller to a "callout" function, which PCRE will then call at specified
161     points during a matching operation. Details are given in the <b>pcrecallout</b>
162     documentation.
163     </P>
164     <br><a name="SEC3" href="#TOC1">MULTITHREADING</a><br>
165     <P>
166     The PCRE functions can be used in multi-threading applications, with the
167     proviso that the memory management functions pointed to by <b>pcre_malloc</b>
168     and <b>pcre_free</b>, and the callout function pointed to by <b>pcre_callout</b>,
169     are shared by all threads.
170     </P>
171     <P>
172     The compiled form of a regular expression is not altered during matching, so
173     the same compiled pattern can safely be used by several threads at once.
174     </P>
175     <br><a name="SEC4" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
176     <P>
177     <b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
178     </P>
179     <P>
180     The function <b>pcre_config()</b> makes it possible for a PCRE client to
181     discover which optional features have been compiled into the PCRE library. The
182     <a href="pcrebuild.html"><b>pcrebuild</b></a>
183     documentation has more details about these optional features.
184     </P>
185     <P>
186     The first argument for <b>pcre_config()</b> is an integer, specifying which
187     information is required; the second argument is a pointer to a variable into
188     which the information is placed. The following information is available:
189     </P>
190     <P>
191     <pre>
193     </PRE>
194     </P>
195     <P>
196     The output is an integer that is set to one if UTF-8 support is available;
197     otherwise it is set to zero.
198     </P>
199     <P>
200     <pre>
202     </PRE>
203     </P>
204     <P>
205     The output is an integer that is set to the value of the code that is used for
206     the newline character. It is either linefeed (10) or carriage return (13), and
207     should normally be the standard character for your operating system.
208     </P>
209     <P>
210     <pre>
212     </PRE>
213     </P>
214     <P>
215     The output is an integer that contains the number of bytes used for internal
216     linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
217     allow larger regular expressions to be compiled, at the expense of slower
218     matching. The default value of 2 is sufficient for all but the most massive
219     patterns, since it allows the compiled pattern to be up to 64K in size.
220     </P>
221     <P>
222     <pre>
224     </PRE>
225     </P>
226     <P>
227     The output is an integer that contains the threshold above which the POSIX
228     interface uses <b>malloc()</b> for output vectors. Further details are given in
229     the <b>pcreposix</b> documentation.
230     </P>
231     <P>
232     <pre>
234     </PRE>
235     </P>
236     <P>
237     The output is an integer that gives the default limit for the number of
238     internal matching function calls in a <b>pcre_exec()</b> execution. Further
239     details are given with <b>pcre_exec()</b> below.
240     </P>
241     <br><a name="SEC5" href="#TOC1">COMPILING A PATTERN</a><br>
242     <P>
243     <b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
244     <b>const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
245     <b>const unsigned char *<i>tableptr</i>);</b>
246     </P>
247     <P>
248     The function <b>pcre_compile()</b> is called to compile a pattern into an
249     internal form. The pattern is a C string terminated by a binary zero, and
250     is passed in the argument <i>pattern</i>. A pointer to a single block of memory
251     that is obtained via <b>pcre_malloc</b> is returned. This contains the compiled
252     code and related data. The <b>pcre</b> type is defined for the returned block;
253     this is a typedef for a structure whose contents are not externally defined. It
254     is up to the caller to free the memory when it is no longer required.
255     </P>
256     <P>
257     Although the compiled code of a PCRE regex is relocatable, that is, it does not
258     depend on memory location, the complete <b>pcre</b> data block is not
259     fully relocatable, because it contains a copy of the <i>tableptr</i> argument,
260     which is an address (see below).
261     </P>
262     <P>
263     The <i>options</i> argument contains independent bits that affect the
264     compilation. It should be zero if no options are required. Some of the options,
265     in particular, those that are compatible with Perl, can also be set and unset
266     from within the pattern (see the detailed description of regular expressions
267     in the <b>pcrepattern</b> documentation). For these options, the contents of the
268     <i>options</i> argument specifies their initial settings at the start of
269     compilation and execution. The PCRE_ANCHORED option can be set at the time of
270     matching as well as at compile time.
271     </P>
272     <P>
273     If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
274     Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
275     NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
276     error message. The offset from the start of the pattern to the character where
277     the error was discovered is placed in the variable pointed to by
278     <i>erroffset</i>, which must not be NULL. If it is, an immediate error is given.
279     </P>
280     <P>
281     If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
282     character tables which are built when it is compiled, using the default C
283     locale. Otherwise, <i>tableptr</i> must be the result of a call to
284     <b>pcre_maketables()</b>. See the section on locale support below.
285     </P>
286     <P>
287     This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
288     </P>
289     <P>
290     <pre>
291     pcre *re;
292     const char *error;
293     int erroffset;
294     re = pcre_compile(
295     "^A.*Z", /* the pattern */
296     0, /* default options */
297     &error, /* for error message */
298     &erroffset, /* for error offset */
299     NULL); /* use default character tables */
300     </PRE>
301     </P>
302     <P>
303     The following option bits are defined:
304     </P>
305     <P>
306     <pre>
308     </PRE>
309     </P>
310     <P>
311     If this bit is set, the pattern is forced to be "anchored", that is, it is
312     constrained to match only at the first matching point in the string which is
313     being searched (the "subject string"). This effect can also be achieved by
314     appropriate constructs in the pattern itself, which is the only way to do it in
315     Perl.
316     </P>
317     <P>
318     <pre>
320     </PRE>
321     </P>
322     <P>
323     If this bit is set, letters in the pattern match both upper and lower case
324     letters. It is equivalent to Perl's /i option, and it can be changed within a
325     pattern by a (?i) option setting.
326     </P>
327     <P>
328     <pre>
330     </PRE>
331     </P>
332     <P>
333     If this bit is set, a dollar metacharacter in the pattern matches only at the
334     end of the subject string. Without this option, a dollar also matches
335     immediately before the final character if it is a newline (but not before any
336     other newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is
337     set. There is no equivalent to this option in Perl, and no way to set it within
338     a pattern.
339     </P>
340     <P>
341     <pre>
343     </PRE>
344     </P>
345     <P>
346     If this bit is set, a dot metacharater in the pattern matches all characters,
347     including newlines. Without it, newlines are excluded. This option is
348     equivalent to Perl's /s option, and it can be changed within a pattern by a
349     (?s) option setting. A negative class such as [^a] always matches a newline
350     character, independent of the setting of this option.
351     </P>
352     <P>
353     <pre>
355     </PRE>
356     </P>
357     <P>
358     If this bit is set, whitespace data characters in the pattern are totally
359     ignored except when escaped or inside a character class. Whitespace does not
360     include the VT character (code 11). In addition, characters between an
361     unescaped # outside a character class and the next newline character,
362     inclusive, are also ignored. This is equivalent to Perl's /x option, and it can
363     be changed within a pattern by a (?x) option setting.
364     </P>
365     <P>
366     This option makes it possible to include comments inside complicated patterns.
367     Note, however, that this applies only to data characters. Whitespace characters
368     may never appear within special character sequences in a pattern, for example
369     within the sequence (?( which introduces a conditional subpattern.
370     </P>
371     <P>
372     <pre>
373     PCRE_EXTRA
374     </PRE>
375     </P>
376     <P>
377     This option was invented in order to turn on additional functionality of PCRE
378     that is incompatible with Perl, but it is currently of very little use. When
379     set, any backslash in a pattern that is followed by a letter that has no
380     special meaning causes an error, thus reserving these combinations for future
381     expansion. By default, as in Perl, a backslash followed by a letter with no
382     special meaning is treated as a literal. There are at present no other features
383     controlled by this option. It can also be set by a (?X) option setting within a
384     pattern.
385     </P>
386     <P>
387     <pre>
389     </PRE>
390     </P>
391     <P>
392     By default, PCRE treats the subject string as consisting of a single "line" of
393     characters (even if it actually contains several newlines). The "start of line"
394     metacharacter (^) matches only at the start of the string, while the "end of
395     line" metacharacter ($) matches only at the end of the string, or before a
396     terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
397     Perl.
398     </P>
399     <P>
400     When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
401     match immediately following or immediately before any newline in the subject
402     string, respectively, as well as at the very start and end. This is equivalent
403     to Perl's /m option, and it can be changed within a pattern by a (?m) option
404     setting. If there are no "\n" characters in a subject string, or no
405     occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
406     </P>
407     <P>
408     <pre>
410     </PRE>
411     </P>
412     <P>
413     If this option is set, it disables the use of numbered capturing parentheses in
414     the pattern. Any opening parenthesis that is not followed by ? behaves as if it
415     were followed by ?: but named parentheses can still be used for capturing (and
416     they acquire numbers in the usual way). There is no equivalent of this option
417     in Perl.
418     </P>
419     <P>
420     <pre>
422     </PRE>
423     </P>
424     <P>
425     This option inverts the "greediness" of the quantifiers so that they are not
426     greedy by default, but become greedy if followed by "?". It is not compatible
427     with Perl. It can also be set by a (?U) option setting within the pattern.
428     </P>
429     <P>
430     <pre>
431     PCRE_UTF8
432     </PRE>
433     </P>
434     <P>
435     This option causes PCRE to regard both the pattern and the subject as strings
436     of UTF-8 characters instead of single-byte character strings. However, it is
437     available only if PCRE has been built to include UTF-8 support. If not, the use
438     of this option provokes an error. Details of how this option changes the
439     behaviour of PCRE are given in the
440     <a href="pcre.html#utf8support">section on UTF-8 support</a>
441     in the main
442     <a href="pcre.html"><b>pcre</b></a>
443     page.
444     </P>
445 nigel 71 <P>
446     <pre>
448     </PRE>
449     </P>
450     <P>
451     When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
452     automatically checked. If an invalid UTF-8 sequence of bytes is found,
453     <b>pcre_compile()</b> returns an error. If you already know that your pattern is
454     valid, and you want to skip this check for performance reasons, you can set the
455     PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
456     UTF-8 string as a pattern is undefined. It may cause your program to crash.
457     Note that there is a similar option for suppressing the checking of subject
458     strings passed to <b>pcre_exec()</b>.
459     </P>
460 nigel 63 <br><a name="SEC6" href="#TOC1">STUDYING A PATTERN</a><br>
461     <P>
462     <b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
463     <b>const char **<i>errptr</i>);</b>
464     </P>
465     <P>
466     When a pattern is going to be used several times, it is worth spending more
467     time analyzing it in order to speed up the time taken for matching. The
468     function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
469     argument. If studing the pattern produces additional information that will help
470     speed up matching, <b>pcre_study()</b> returns a pointer to a <b>pcre_extra</b>
471     block, in which the <i>study_data</i> field points to the results of the study.
472     </P>
473     <P>
474     The returned value from a <b>pcre_study()</b> can be passed directly to
475     <b>pcre_exec()</b>. However, the <b>pcre_extra</b> block also contains other
476     fields that can be set by the caller before the block is passed; these are
477     described below. If studying the pattern does not produce any additional
478     information, <b>pcre_study()</b> returns NULL. In that circumstance, if the
479     calling program wants to pass some of the other fields to <b>pcre_exec()</b>, it
480     must set up its own <b>pcre_extra</b> block.
481     </P>
482     <P>
483     The second argument contains option bits. At present, no options are defined
484     for <b>pcre_study()</b>, and this argument should always be zero.
485     </P>
486     <P>
487     The third argument for <b>pcre_study()</b> is a pointer for an error message. If
488     studying succeeds (even if no data is returned), the variable it points to is
489     set to NULL. Otherwise it points to a textual error message. You should
490     therefore test the error pointer for NULL after calling <b>pcre_study()</b>, to
491     be sure that it has run successfully.
492     </P>
493     <P>
494     This is a typical call to <b>pcre_study</b>():
495     </P>
496     <P>
497     <pre>
498     pcre_extra *pe;
499     pe = pcre_study(
500     re, /* result of pcre_compile() */
501     0, /* no options exist */
502     &error); /* set to NULL or points to a message */
503     </PRE>
504     </P>
505     <P>
506     At present, studying a pattern is useful only for non-anchored patterns that do
507     not have a single fixed starting character. A bitmap of possible starting
508     characters is created.
509     </P>
510     <a name="localesupport"></a><br><a name="SEC7" href="#TOC1">LOCALE SUPPORT</a><br>
511     <P>
512     PCRE handles caseless matching, and determines whether characters are letters,
513     digits, or whatever, by reference to a set of tables. When running in UTF-8
514     mode, this applies only to characters with codes less than 256. The library
515     contains a default set of tables that is created in the default C locale when
516     PCRE is compiled. This is used when the final argument of <b>pcre_compile()</b>
517     is NULL, and is sufficient for many applications.
518     </P>
519     <P>
520     An alternative set of tables can, however, be supplied. Such tables are built
521     by calling the <b>pcre_maketables()</b> function, which has no arguments, in the
522     relevant locale. The result can then be passed to <b>pcre_compile()</b> as often
523     as necessary. For example, to build and use tables that are appropriate for the
524     French locale (where accented characters with codes greater than 128 are
525     treated as letters), the following code could be used:
526     </P>
527     <P>
528     <pre>
529     setlocale(LC_CTYPE, "fr");
530     tables = pcre_maketables();
531     re = pcre_compile(..., tables);
532     </PRE>
533     </P>
534     <P>
535     The tables are built in memory that is obtained via <b>pcre_malloc</b>. The
536     pointer that is passed to <b>pcre_compile</b> is saved with the compiled
537     pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
538     and <b>pcre_exec()</b>. Thus, for any single pattern, compilation, studying and
539     matching all happen in the same locale, but different patterns can be compiled
540     in different locales. It is the caller's responsibility to ensure that the
541     memory containing the tables remains available for as long as it is needed.
542     </P>
543     <br><a name="SEC8" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
544     <P>
545     <b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
546     <b>int <i>what</i>, void *<i>where</i>);</b>
547     </P>
548     <P>
549     The <b>pcre_fullinfo()</b> function returns information about a compiled
550     pattern. It replaces the obsolete <b>pcre_info()</b> function, which is
551     nevertheless retained for backwards compability (and is documented below).
552     </P>
553     <P>
554     The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
555     pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
556     the pattern was not studied. The third argument specifies which piece of
557     information is required, and the fourth argument is a pointer to a variable
558     to receive the data. The yield of the function is zero for success, or one of
559     the following negative numbers:
560     </P>
561     <P>
562     <pre>
563     PCRE_ERROR_NULL the argument <i>code</i> was NULL
564     the argument <i>where</i> was NULL
565     PCRE_ERROR_BADMAGIC the "magic number" was not found
566     PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
567     </PRE>
568     </P>
569     <P>
570     Here is a typical call of <b>pcre_fullinfo()</b>, to obtain the length of the
571     compiled pattern:
572     </P>
573     <P>
574     <pre>
575     int rc;
576     unsigned long int length;
577     rc = pcre_fullinfo(
578     re, /* result of pcre_compile() */
579     pe, /* result of pcre_study(), or NULL */
580     PCRE_INFO_SIZE, /* what is required */
581     &length); /* where to put the data */
582     </PRE>
583     </P>
584     <P>
585     The possible values for the third argument are defined in <b>pcre.h</b>, and are
586     as follows:
587     </P>
588     <P>
589     <pre>
591     </PRE>
592     </P>
593     <P>
594     Return the number of the highest back reference in the pattern. The fourth
595     argument should point to an <b>int</b> variable. Zero is returned if there are
596     no back references.
597     </P>
598     <P>
599     <pre>
601     </PRE>
602     </P>
603     <P>
604     Return the number of capturing subpatterns in the pattern. The fourth argument
605     should point to an \fbint\fR variable.
606     </P>
607     <P>
608     <pre>
610     </PRE>
611     </P>
612     <P>
613     Return information about the first byte of any matched string, for a
614     non-anchored pattern. (This option used to be called PCRE_INFO_FIRSTCHAR; the
615     old name is still recognized for backwards compatibility.)
616     </P>
617     <P>
618     If there is a fixed first byte, e.g. from a pattern such as (cat|cow|coyote),
619     it is returned in the integer pointed to by <i>where</i>. Otherwise, if either
620     </P>
621     <P>
622     (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
623     starts with "^", or
624     </P>
625     <P>
626     (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
627     (if it were set, the pattern would be anchored),
628     </P>
629     <P>
630     -1 is returned, indicating that the pattern matches only at the start of a
631     subject string or after any newline within the string. Otherwise -2 is
632     returned. For anchored patterns, -2 is returned.
633     </P>
634     <P>
635     <pre>
637     </PRE>
638     </P>
639     <P>
640     If the pattern was studied, and this resulted in the construction of a 256-bit
641     table indicating a fixed set of bytes for the first byte in any matching
642     string, a pointer to the table is returned. Otherwise NULL is returned. The
643     fourth argument should point to an <b>unsigned char *</b> variable.
644     </P>
645     <P>
646     <pre>
648     </PRE>
649     </P>
650     <P>
651 nigel 65 Return the value of the rightmost literal byte that must exist in any matched
652     string, other than at its start, if such a byte has been recorded. The fourth
653     argument should point to an <b>int</b> variable. If there is no such byte, -1 is
654     returned. For anchored patterns, a last literal byte is recorded only if it
655     follows something of variable length. For example, for the pattern
656     /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
657     is -1.
658 nigel 63 </P>
659     <P>
660     <pre>
664     </PRE>
665     </P>
666     <P>
667     PCRE supports the use of named as well as numbered capturing parentheses. The
668     names are just an additional way of identifying the parentheses, which still
669     acquire a number. A caller that wants to extract data from a named subpattern
670     must convert the name to a number in order to access the correct pointers in
671     the output vector (described with <b>pcre_exec()</b> below). In order to do
672     this, it must first use these three values to obtain the name-to-number mapping
673     table for the pattern.
674     </P>
675     <P>
676     The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
677     the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
678     entry; both of these return an <b>int</b> value. The entry size depends on the
679     length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
680     entry of the table (a pointer to <b>char</b>). The first two bytes of each entry
681     are the number of the capturing parenthesis, most significant byte first. The
682     rest of the entry is the corresponding name, zero terminated. The names are in
683     alphabetical order. For example, consider the following pattern (assume
684     PCRE_EXTENDED is set, so white space - including newlines - is ignored):
685     </P>
686     <P>
687     <pre>
688     (?P&#60;date&#62; (?P&#60;year&#62;(\d\d)?\d\d) -
689     (?P&#60;month&#62;\d\d) - (?P&#60;day&#62;\d\d) )
690     </PRE>
691     </P>
692     <P>
693     There are four named subpatterns, so the table has four entries, and each entry
694     in the table is eight bytes long. The table is as follows, with non-printing
695     bytes shows in hex, and undefined bytes shown as ??:
696     </P>
697     <P>
698     <pre>
699     00 01 d a t e 00 ??
700     00 05 d a y 00 ?? ??
701     00 04 m o n t h 00
702     00 02 y e a r 00 ??
703     </PRE>
704     </P>
705     <P>
706     When writing code to extract data from named subpatterns, remember that the
707     length of each entry may be different for each compiled pattern.
708     </P>
709     <P>
710     <pre>
712     </PRE>
713     </P>
714     <P>
715     Return a copy of the options with which the pattern was compiled. The fourth
716     argument should point to an <b>unsigned long int</b> variable. These option bits
717     are those specified in the call to <b>pcre_compile()</b>, modified by any
718     top-level option settings within the pattern itself.
719     </P>
720     <P>
721     A pattern is automatically anchored by PCRE if all of its top-level
722     alternatives begin with one of the following:
723     </P>
724     <P>
725     <pre>
726     ^ unless PCRE_MULTILINE is set
727     \A always
728     \G always
729     .* if PCRE_DOTALL is set and there are no back
730     references to the subpattern in which .* appears
731     </PRE>
732     </P>
733     <P>
734     For such patterns, the PCRE_ANCHORED bit is set in the options returned by
735     <b>pcre_fullinfo()</b>.
736     </P>
737     <P>
738     <pre>
740     </PRE>
741     </P>
742     <P>
743     Return the size of the compiled pattern, that is, the value that was passed as
744     the argument to <b>pcre_malloc()</b> when PCRE was getting memory in which to
745     place the compiled data. The fourth argument should point to a <b>size_t</b>
746     variable.
747     </P>
748     <P>
749     <pre>
751     </PRE>
752     </P>
753     <P>
754     Returns the size of the data block pointed to by the <i>study_data</i> field in
755     a <b>pcre_extra</b> block. That is, it is the value that was passed to
756     <b>pcre_malloc()</b> when PCRE was getting memory into which to place the data
757     created by <b>pcre_study()</b>. The fourth argument should point to a
758     <b>size_t</b> variable.
759     </P>
760     <br><a name="SEC9" href="#TOC1">OBSOLETE INFO FUNCTION</a><br>
761     <P>
762     <b>int pcre_info(const pcre *<i>code</i>, int *<i>optptr</i>, int</b>
763     <b>*<i>firstcharptr</i>);</b>
764     </P>
765     <P>
766     The <b>pcre_info()</b> function is now obsolete because its interface is too
767     restrictive to return all the available data about a compiled pattern. New
768     programs should use <b>pcre_fullinfo()</b> instead. The yield of
769     <b>pcre_info()</b> is the number of capturing subpatterns, or one of the
770     following negative numbers:
771     </P>
772     <P>
773     <pre>
774     PCRE_ERROR_NULL the argument <i>code</i> was NULL
775     PCRE_ERROR_BADMAGIC the "magic number" was not found
776     </PRE>
777     </P>
778     <P>
779     If the <i>optptr</i> argument is not NULL, a copy of the options with which the
780     pattern was compiled is placed in the integer it points to (see
781     PCRE_INFO_OPTIONS above).
782     </P>
783     <P>
784     If the pattern is not anchored and the <i>firstcharptr</i> argument is not NULL,
785     it is used to pass back information about the first character of any matched
786     string (see PCRE_INFO_FIRSTBYTE above).
787     </P>
788     <br><a name="SEC10" href="#TOC1">MATCHING A PATTERN</a><br>
789     <P>
790     <b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
791     <b>const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
792     <b>int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
793     </P>
794     <P>
795     The function <b>pcre_exec()</b> is called to match a subject string against a
796     pre-compiled pattern, which is passed in the <i>code</i> argument. If the
797     pattern has been studied, the result of the study should be passed in the
798     <i>extra</i> argument.
799     </P>
800     <P>
801     Here is an example of a simple call to <b>pcre_exec()</b>:
802     </P>
803     <P>
804     <pre>
805     int rc;
806     int ovector[30];
807     rc = pcre_exec(
808     re, /* result of pcre_compile() */
809     NULL, /* we didn't study the pattern */
810     "some string", /* the subject string */
811     11, /* the length of the subject string */
812     0, /* start at offset 0 in the subject */
813     0, /* default options */
814     ovector, /* vector for substring information */
815     30); /* number of elements in the vector */
816     </PRE>
817     </P>
818     <P>
819     If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
820     data block. The <b>pcre_study()</b> function returns such a block (when it
821     doesn't return NULL), but you can also create one for yourself, and pass
822     additional information in it. The fields in the block are as follows:
823     </P>
824     <P>
825     <pre>
826     unsigned long int <i>flags</i>;
827     void *<i>study_data</i>;
828     unsigned long int <i>match_limit</i>;
829     void *<i>callout_data</i>;
830     </PRE>
831     </P>
832     <P>
833     The <i>flags</i> field is a bitmap that specifies which of the other fields
834     are set. The flag bits are:
835     </P>
836     <P>
837     <pre>
841     </PRE>
842     </P>
843     <P>
844     Other flag bits should be set to zero. The <i>study_data</i> field is set in the
845     <b>pcre_extra</b> block that is returned by <b>pcre_study()</b>, together with
846     the appropriate flag bit. You should not set this yourself, but you can add to
847     the block by setting the other fields.
848     </P>
849     <P>
850     The <i>match_limit</i> field provides a means of preventing PCRE from using up a
851     vast amount of resources when running patterns that are not going to match,
852     but which have a very large number of possibilities in their search trees. The
853     classic example is the use of nested unlimited repeats. Internally, PCRE uses a
854     function called <b>match()</b> which it calls repeatedly (sometimes
855     recursively). The limit is imposed on the number of times this function is
856     called during a match, which has the effect of limiting the amount of recursion
857     and backtracking that can take place. For patterns that are not anchored, the
858     count starts from zero for each position in the subject string.
859     </P>
860     <P>
861     The default limit for the library can be set when PCRE is built; the default
862     default is 10 million, which handles all but the most extreme cases. You can
863     reduce the default by suppling <b>pcre_exec()</b> with a \fRpcre_extra\fR block
864     in which <i>match_limit</i> is set to a smaller value, and
865     PCRE_EXTRA_MATCH_LIMIT is set in the <i>flags</i> field. If the limit is
866     exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_MATCHLIMIT.
867     </P>
868     <P>
869     The <i>pcre_callout</i> field is used in conjunction with the "callout" feature,
870     which is described in the <b>pcrecallout</b> documentation.
871     </P>
872     <P>
873     The PCRE_ANCHORED option can be passed in the <i>options</i> argument, whose
874     unused bits must be zero. This limits <b>pcre_exec()</b> to matching at the
875     first matching position. However, if a pattern was compiled with PCRE_ANCHORED,
876     or turned out to be anchored by virtue of its contents, it cannot be made
877     unachored at matching time.
878     </P>
879     <P>
880 nigel 71 When PCRE_UTF8 was set at compile time, the validity of the subject as a UTF-8
881     string is automatically checked. If an invalid UTF-8 sequence of bytes is
882     found, <b>pcre_exec()</b> returns the error PCRE_ERROR_BADUTF8. If you already
883     know that your subject is valid, and you want to skip this check for
884     performance reasons, you can set the PCRE_NO_UTF8_CHECK option when calling
885     <b>pcre_exec()</b>. When this option is set, the effect of passing an invalid
886     UTF-8 string as a subject is undefined. It may cause your program to crash.
887     </P>
888     <P>
889 nigel 63 There are also three further options that can be set only at matching time:
890     </P>
891     <P>
892     <pre>
894     </PRE>
895     </P>
896     <P>
897     The first character of the string is not the beginning of a line, so the
898     circumflex metacharacter should not match before it. Setting this without
899     PCRE_MULTILINE (at compile time) causes circumflex never to match.
900     </P>
901     <P>
902     <pre>
904     </PRE>
905     </P>
906     <P>
907     The end of the string is not the end of a line, so the dollar metacharacter
908     should not match it nor (except in multiline mode) a newline immediately before
909     it. Setting this without PCRE_MULTILINE (at compile time) causes dollar never
910     to match.
911     </P>
912     <P>
913     <pre>
915     </PRE>
916     </P>
917     <P>
918     An empty string is not considered to be a valid match if this option is set. If
919     there are alternatives in the pattern, they are tried. If all the alternatives
920     match the empty string, the entire match fails. For example, if the pattern
921     </P>
922     <P>
923     <pre>
924     a?b?
925     </PRE>
926     </P>
927     <P>
928     is applied to a string not beginning with "a" or "b", it matches the empty
929     string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
930     valid, so PCRE searches further into the string for occurrences of "a" or "b".
931     </P>
932     <P>
933     Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
934     of a pattern match of the empty string within its <b>split()</b> function, and
935     when using the /g modifier. It is possible to emulate Perl's behaviour after
936     matching a null string by first trying the match again at the same offset with
937     PCRE_NOTEMPTY set, and then if that fails by advancing the starting offset (see
938     below) and trying an ordinary match again.
939     </P>
940     <P>
941     The subject string is passed to <b>pcre_exec()</b> as a pointer in
942     <i>subject</i>, a length in <i>length</i>, and a starting offset in
943     <i>startoffset</i>. Unlike the pattern string, the subject may contain binary
944     zero bytes. When the starting offset is zero, the search for a match starts at
945     the beginning of the subject, and this is by far the most common case.
946     </P>
947     <P>
948     If the pattern was compiled with the PCRE_UTF8 option, the subject must be a
949     sequence of bytes that is a valid UTF-8 string. If an invalid UTF-8 string is
950     passed, PCRE's behaviour is not defined.
951     </P>
952     <P>
953     A non-zero starting offset is useful when searching for another match in the
954     same subject by calling <b>pcre_exec()</b> again after a previous success.
955     Setting <i>startoffset</i> differs from just passing over a shortened string and
956     setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
957     lookbehind. For example, consider the pattern
958     </P>
959     <P>
960     <pre>
961     \Biss\B
962     </PRE>
963     </P>
964     <P>
965     which finds occurrences of "iss" in the middle of words. (\B matches only if
966     the current position in the subject is not a word boundary.) When applied to
967     the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
968     occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
969     subject, namely "issipi", it does not match, because \B is always false at the
970     start of the subject, which is deemed to be a word boundary. However, if
971     <b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
972     set to 4, it finds the second occurrence of "iss" because it is able to look
973     behind the starting point to discover that it is preceded by a letter.
974     </P>
975     <P>
976     If a non-zero starting offset is passed when the pattern is anchored, one
977     attempt to match at the given offset is tried. This can only succeed if the
978     pattern does not require the match to be at the start of the subject.
979     </P>
980     <P>
981     In general, a pattern matches a certain portion of the subject, and in
982     addition, further substrings from the subject may be picked out by parts of the
983     pattern. Following the usage in Jeffrey Friedl's book, this is called
984     "capturing" in what follows, and the phrase "capturing subpattern" is used for
985     a fragment of a pattern that picks out a substring. PCRE supports several other
986     kinds of parenthesized subpattern that do not cause substrings to be captured.
987     </P>
988     <P>
989     Captured substrings are returned to the caller via a vector of integer offsets
990     whose address is passed in <i>ovector</i>. The number of elements in the vector
991     is passed in <i>ovecsize</i>. The first two-thirds of the vector is used to pass
992     back captured substrings, each substring using a pair of integers. The
993     remaining third of the vector is used as workspace by <b>pcre_exec()</b> while
994     matching capturing subpatterns, and is not available for passing back
995     information. The length passed in <i>ovecsize</i> should always be a multiple of
996     three. If it is not, it is rounded down.
997     </P>
998     <P>
999     When a match has been successful, information about captured substrings is
1000     returned in pairs of integers, starting at the beginning of <i>ovector</i>, and
1001     continuing up to two-thirds of its length at the most. The first element of a
1002     pair is set to the offset of the first character in a substring, and the second
1003     is set to the offset of the first character after the end of a substring. The
1004     first pair, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the portion of the
1005     subject string matched by the entire pattern. The next pair is used for the
1006     first capturing subpattern, and so on. The value returned by <b>pcre_exec()</b>
1007     is the number of pairs that have been set. If there are no capturing
1008     subpatterns, the return value from a successful match is 1, indicating that
1009     just the first pair of offsets has been set.
1010     </P>
1011     <P>
1012     Some convenience functions are provided for extracting the captured substrings
1013     as separate strings. These are described in the following section.
1014     </P>
1015     <P>
1016     It is possible for an capturing subpattern number <i>n+1</i> to match some
1017     part of the subject when subpattern <i>n</i> has not been used at all. For
1018     example, if the string "abc" is matched against the pattern (a|(z))(bc)
1019     subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset
1020     values corresponding to the unused subpattern are set to -1.
1021     </P>
1022     <P>
1023     If a capturing subpattern is matched repeatedly, it is the last portion of the
1024     string that it matched that gets returned.
1025     </P>
1026     <P>
1027     If the vector is too small to hold all the captured substrings, it is used as
1028     far as possible (up to two-thirds of its length), and the function returns a
1029     value of zero. In particular, if the substring offsets are not of interest,
1030     <b>pcre_exec()</b> may be called with <i>ovector</i> passed as NULL and
1031     <i>ovecsize</i> as zero. However, if the pattern contains back references and
1032     the <i>ovector</i> isn't big enough to remember the related substrings, PCRE has
1033     to get additional memory for use during matching. Thus it is usually advisable
1034     to supply an <i>ovector</i>.
1035     </P>
1036     <P>
1037     Note that <b>pcre_info()</b> can be used to find out how many capturing
1038     subpatterns there are in a compiled pattern. The smallest size for
1039     <i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
1040     the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
1041     </P>
1042     <P>
1043     If <b>pcre_exec()</b> fails, it returns a negative number. The following are
1044     defined in the header file:
1045     </P>
1046     <P>
1047     <pre>
1048     PCRE_ERROR_NOMATCH (-1)
1049     </PRE>
1050     </P>
1051     <P>
1052     The subject string did not match the pattern.
1053     </P>
1054     <P>
1055     <pre>
1056     PCRE_ERROR_NULL (-2)
1057     </PRE>
1058     </P>
1059     <P>
1060     Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
1061     NULL and <i>ovecsize</i> was not zero.
1062     </P>
1063     <P>
1064     <pre>
1066     </PRE>
1067     </P>
1068     <P>
1069     An unrecognized bit was set in the <i>options</i> argument.
1070     </P>
1071     <P>
1072     <pre>
1074     </PRE>
1075     </P>
1076     <P>
1077     PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1078     the case when it is passed a junk pointer. This is the error it gives when the
1079     magic number isn't present.
1080     </P>
1081     <P>
1082     <pre>
1084     </PRE>
1085     </P>
1086     <P>
1087     While running the pattern match, an unknown item was encountered in the
1088     compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1089     of the compiled pattern.
1090     </P>
1091     <P>
1092     <pre>
1094     </PRE>
1095     </P>
1096     <P>
1097     If a pattern contains back references, but the <i>ovector</i> that is passed to
1098     <b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
1099     gets a block of memory at the start of matching to use for this purpose. If the
1100     call via <b>pcre_malloc()</b> fails, this error is given. The memory is freed at
1101     the end of matching.
1102     </P>
1103     <P>
1104     <pre>
1106     </PRE>
1107     </P>
1108     <P>
1109     This error is used by the <b>pcre_copy_substring()</b>,
1110     <b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
1111     below). It is never returned by <b>pcre_exec()</b>.
1112     </P>
1113     <P>
1114     <pre>
1116     </PRE>
1117     </P>
1118     <P>
1119     The recursion and backtracking limit, as specified by the <i>match_limit</i>
1120     field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
1121     description above.
1122     </P>
1123     <P>
1124     <pre>
1125     PCRE_ERROR_CALLOUT (-9)
1126     </PRE>
1127     </P>
1128     <P>
1129     This error is never generated by <b>pcre_exec()</b> itself. It is provided for
1130     use by callout functions that want to yield a distinctive error code. See the
1131     <b>pcrecallout</b> documentation for details.
1132     </P>
1133 nigel 71 <P>
1134     <pre>
1135     PCRE_ERROR_BADUTF8 (-10)
1136     </PRE>
1137     </P>
1138     <P>
1139     A string that contains an invalid UTF-8 byte sequence was passed as a subject.
1140     </P>
1141 nigel 63 <br><a name="SEC11" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
1142     <P>
1143     <b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1144     <b>int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
1145     <b>int <i>buffersize</i>);</b>
1146     </P>
1147     <P>
1148     <b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
1149     <b>int <i>stringcount</i>, int <i>stringnumber</i>,</b>
1150     <b>const char **<i>stringptr</i>);</b>
1151     </P>
1152     <P>
1153     <b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
1154     <b>int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
1155     </P>
1156     <P>
1157     Captured substrings can be accessed directly by using the offsets returned by
1158     <b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
1159     <b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
1160     <b>pcre_get_substring_list()</b> are provided for extracting captured substrings
1161     as new, separate, zero-terminated strings. These functions identify substrings
1162     by number. The next section describes functions for extracting named
1163     substrings. A substring that contains a binary zero is correctly extracted and
1164     has a further zero added on the end, but the result is not, of course,
1165     a C string.
1166     </P>
1167     <P>
1168     The first three arguments are the same for all three of these functions:
1169     <i>subject</i> is the subject string which has just been successfully matched,
1170     <i>ovector</i> is a pointer to the vector of integer offsets that was passed to
1171     <b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
1172     captured by the match, including the substring that matched the entire regular
1173     expression. This is the value returned by <b>pcre_exec</b> if it is greater than
1174     zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of space
1175     in <i>ovector</i>, the value passed as <i>stringcount</i> should be the size of
1176     the vector divided by three.
1177     </P>
1178     <P>
1179     The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
1180     extract a single substring, whose number is given as <i>stringnumber</i>. A
1181     value of zero extracts the substring that matched the entire pattern, while
1182     higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
1183     the string is placed in <i>buffer</i>, whose length is given by
1184     <i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
1185     obtained via <b>pcre_malloc</b>, and its address is returned via
1186     <i>stringptr</i>. The yield of the function is the length of the string, not
1187     including the terminating zero, or one of
1188     </P>
1189     <P>
1190     <pre>
1192     </PRE>
1193     </P>
1194     <P>
1195     The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
1196     memory failed for <b>pcre_get_substring()</b>.
1197     </P>
1198     <P>
1199     <pre>
1201     </PRE>
1202     </P>
1203     <P>
1204     There is no substring whose number is <i>stringnumber</i>.
1205     </P>
1206     <P>
1207     The <b>pcre_get_substring_list()</b> function extracts all available substrings
1208     and builds a list of pointers to them. All this is done in a single block of
1209     memory which is obtained via <b>pcre_malloc</b>. The address of the memory block
1210     is returned via <i>listptr</i>, which is also the start of the list of string
1211     pointers. The end of the list is marked by a NULL pointer. The yield of the
1212     function is zero if all went well, or
1213     </P>
1214     <P>
1215     <pre>
1217     </PRE>
1218     </P>
1219     <P>
1220     if the attempt to get the memory block failed.
1221     </P>
1222     <P>
1223     When any of these functions encounter a substring that is unset, which can
1224     happen when capturing subpattern number <i>n+1</i> matches some part of the
1225     subject, but subpattern <i>n</i> has not been used at all, they return an empty
1226     string. This can be distinguished from a genuine zero-length substring by
1227     inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
1228     substrings.
1229     </P>
1230     <P>
1231     The two convenience functions <b>pcre_free_substring()</b> and
1232     <b>pcre_free_substring_list()</b> can be used to free the memory returned by
1233     a previous call of <b>pcre_get_substring()</b> or
1234     <b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
1235     the function pointed to by <b>pcre_free</b>, which of course could be called
1236     directly from a C program. However, PCRE is used in some situations where it is
1237     linked via a special interface to another programming language which cannot use
1238     <b>pcre_free</b> directly; it is for these cases that the functions are
1239     provided.
1240     </P>
1241     <br><a name="SEC12" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
1242     <P>
1243     <b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
1244     <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1245     <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1246     <b>char *<i>buffer</i>, int <i>buffersize</i>);</b>
1247     </P>
1248     <P>
1249     <b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
1250     <b>const char *<i>name</i>);</b>
1251     </P>
1252     <P>
1253     <b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
1254     <b>const char *<i>subject</i>, int *<i>ovector</i>,</b>
1255     <b>int <i>stringcount</i>, const char *<i>stringname</i>,</b>
1256     <b>const char **<i>stringptr</i>);</b>
1257     </P>
1258     <P>
1259     To extract a substring by name, you first have to find associated number. This
1260     can be done by calling <b>pcre_get_stringnumber()</b>. The first argument is the
1261     compiled pattern, and the second is the name. For example, for this pattern
1262     </P>
1263     <P>
1264     <pre>
1265     ab(?&#60;xxx&#62;\d+)...
1266     </PRE>
1267     </P>
1268     <P>
1269     the number of the subpattern called "xxx" is 1. Given the number, you can then
1270     extract the substring directly, or use one of the functions described in the
1271     previous section. For convenience, there are also two functions that do the
1272     whole job.
1273     </P>
1274     <P>
1275     Most of the arguments of <i>pcre_copy_named_substring()</i> and
1276     <i>pcre_get_named_substring()</i> are the same as those for the functions that
1277     extract by number, and so are not re-described here. There are just two
1278     differences.
1279     </P>
1280     <P>
1281     First, instead of a substring number, a substring name is given. Second, there
1282     is an extra argument, given at the start, which is a pointer to the compiled
1283     pattern. This is needed in order to gain access to the name-to-number
1284     translation table.
1285     </P>
1286     <P>
1287     These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
1288     then call <i>pcre_copy_substring()</i> or <i>pcre_get_substring()</i>, as
1289     appropriate.
1290     </P>
1291     <P>
1292 nigel 71 Last updated: 20 August 2003
1293 nigel 63 <br>
1294     Copyright &copy; 1997-2003 University of Cambridge.

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