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revision 440 by ph10, Wed Sep 9 10:14:40 2009 UTC revision 456 by ph10, Fri Oct 2 08:53:31 2009 UTC
# Line 395  avoiding the use of the stack. Line 395  avoiding the use of the stack.
395  Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be  Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be
396  called to compile a pattern into an internal form. The only difference between  called to compile a pattern into an internal form. The only difference between
397  the two interfaces is that \fBpcre_compile2()\fP has an additional argument,  the two interfaces is that \fBpcre_compile2()\fP has an additional argument,
398  \fIerrorcodeptr\fP, via which a numerical error code can be returned.  \fIerrorcodeptr\fP, via which a numerical error code can be returned. To avoid
399    too much repetition, we refer just to \fBpcre_compile()\fP below, but the
400    information applies equally to \fBpcre_compile2()\fP.
401  .P  .P
402  The pattern is a C string terminated by a binary zero, and is passed in the  The pattern is a C string terminated by a binary zero, and is passed in the
403  \fIpattern\fP argument. A pointer to a single block of memory that is obtained  \fIpattern\fP argument. A pointer to a single block of memory that is obtained
# Line 412  argument, which is an address (see below Line 414  argument, which is an address (see below
414  The \fIoptions\fP argument contains various bit settings that affect the  The \fIoptions\fP argument contains various bit settings that affect the
415  compilation. It should be zero if no options are required. The available  compilation. It should be zero if no options are required. The available
416  options are described below. Some of them (in particular, those that are  options are described below. Some of them (in particular, those that are
417  compatible with Perl, but also some others) can also be set and unset from  compatible with Perl, but some others as well) can also be set and unset from
418  within the pattern (see the detailed description in the  within the pattern (see the detailed description in the
419  .\" HREF  .\" HREF
420  \fBpcrepattern\fP  \fBpcrepattern\fP
421  .\"  .\"
422  documentation). For those options that can be different in different parts of  documentation). For those options that can be different in different parts of
423  the pattern, the contents of the \fIoptions\fP argument specifies their initial  the pattern, the contents of the \fIoptions\fP argument specifies their
424  settings at the start of compilation and execution. The PCRE_ANCHORED and  settings at the start of compilation and execution. The PCRE_ANCHORED,
425  PCRE_NEWLINE_\fIxxx\fP options can be set at the time of matching as well as at  PCRE_BSR_\fIxxx\fP, and PCRE_NEWLINE_\fIxxx\fP options can be set at the time
426  compile time.  of matching as well as at compile time.
427  .P  .P
428  If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.  If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
429  Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns  Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
430  NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual  NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual
431  error message. This is a static string that is part of the library. You must  error message. This is a static string that is part of the library. You must
432  not try to free it. The offset from the start of the pattern to the character  not try to free it. The byte offset from the start of the pattern to the
433  where the error was discovered is placed in the variable pointed to by  character that was being processed when the error was discovered is placed in
434  \fIerroffset\fP, which must not be NULL. If it is, an immediate error is given.  the variable pointed to by \fIerroffset\fP, which must not be NULL. If it is,
435    an immediate error is given. Some errors are not detected until checks are
436    carried out when the whole pattern has been scanned; in this case the offset is
437    set to the end of the pattern.
438  .P  .P
439  If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the  If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the
440  \fIerrorcodeptr\fP argument is not NULL, a non-zero error code number is  \fIerrorcodeptr\fP argument is not NULL, a non-zero error code number is
# Line 769  help speed up matching, \fBpcre_study()\ Line 774  help speed up matching, \fBpcre_study()\
774  results of the study.  results of the study.
775  .P  .P
776  The returned value from \fBpcre_study()\fP can be passed directly to  The returned value from \fBpcre_study()\fP can be passed directly to
777  \fBpcre_exec()\fP. However, a \fBpcre_extra\fP block also contains other  \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. However, a \fBpcre_extra\fP block
778  fields that can be set by the caller before the block is passed; these are  also contains other fields that can be set by the caller before the block is
779  described  passed; these are described
780  .\" HTML <a href="#extradata">  .\" HTML <a href="#extradata">
781  .\" </a>  .\" </a>
782  below  below
783  .\"  .\"
784  in the section on matching a pattern.  in the section on matching a pattern.
785  .P  .P
786  If studying the pattern does not produce any additional information  If studying the pattern does not produce any useful information,
787  \fBpcre_study()\fP returns NULL. In that circumstance, if the calling program  \fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
788  wants to pass any of the other fields to \fBpcre_exec()\fP, it must set up its  wants to pass any of the other fields to \fBpcre_exec()\fP or
789  own \fBpcre_extra\fP block.  \fBpcre_dfa_exec()\fP, it must set up its own \fBpcre_extra\fP block.
790  .P  .P
791  The second argument of \fBpcre_study()\fP contains option bits. At present, no  The second argument of \fBpcre_study()\fP contains option bits. At present, no
792  options are defined, and this argument should always be zero.  options are defined, and this argument should always be zero.
# Line 801  This is a typical call to \fBpcre_study\ Line 806  This is a typical call to \fBpcre_study\
806      0,              /* no options exist */      0,              /* no options exist */
807      &error);        /* set to NULL or points to a message */      &error);        /* set to NULL or points to a message */
808  .sp  .sp
809  At present, studying a pattern is useful only for non-anchored patterns that do  Studying a pattern does two things: first, a lower bound for the length of
810  not have a single fixed starting character. A bitmap of possible starting  subject string that is needed to match the pattern is computed. This does not
811  bytes is created.  mean that there are any strings of that length that match, but it does
812    guarantee that no shorter strings match. The value is used by
813    \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP to avoid wasting time by trying to
814    match strings that are shorter than the lower bound. You can find out the value
815    in a calling program via the \fBpcre_fullinfo()\fP function.
816    .P
817    Studying a pattern is also useful for non-anchored patterns that do not have a
818    single fixed starting character. A bitmap of possible starting bytes is
819    created. This speeds up finding a position in the subject at which to start
820    matching.
821  .  .
822  .  .
823  .\" HTML <a name="localesupport"></a>  .\" HTML <a name="localesupport"></a>
# Line 968  follows something of variable length. Fo Line 982  follows something of variable length. Fo
982  /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value  /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
983  is -1.  is -1.
984  .sp  .sp
985      PCRE_INFO_MINLENGTH
986    .sp
987    If the pattern was studied and a minimum length for matching subject strings
988    was computed, its value is returned. Otherwise the returned value is -1. The
989    value is a number of characters, not bytes (this may be relevant in UTF-8
990    mode). The fourth argument should point to an \fBint\fP variable. A
991    non-negative value is a lower bound to the length of any matching string. There
992    may not be any strings of that length that do actually match, but every string
993    that does match is at least that long.
994    .sp
995    PCRE_INFO_NAMECOUNT    PCRE_INFO_NAMECOUNT
996    PCRE_INFO_NAMEENTRYSIZE    PCRE_INFO_NAMEENTRYSIZE
997    PCRE_INFO_NAMETABLE    PCRE_INFO_NAMETABLE
# Line 1056  variable. Line 1080  variable.
1080  Return the size of the data block pointed to by the \fIstudy_data\fP field in  Return the size of the data block pointed to by the \fIstudy_data\fP field in
1081  a \fBpcre_extra\fP block. That is, it is the value that was passed to  a \fBpcre_extra\fP block. That is, it is the value that was passed to
1082  \fBpcre_malloc()\fP when PCRE was getting memory into which to place the data  \fBpcre_malloc()\fP when PCRE was getting memory into which to place the data
1083  created by \fBpcre_study()\fP. The fourth argument should point to a  created by \fBpcre_study()\fP. If \fBpcre_extra\fP is NULL, or there is no
1084    study data, zero is returned. The fourth argument should point to a
1085  \fBsize_t\fP variable.  \fBsize_t\fP variable.
1086  .  .
1087  .  .
# Line 1118  is different. (This seems a highly unlik Line 1143  is different. (This seems a highly unlik
1143  .P  .P
1144  The function \fBpcre_exec()\fP is called to match a subject string against a  The function \fBpcre_exec()\fP is called to match a subject string against a
1145  compiled pattern, which is passed in the \fIcode\fP argument. If the  compiled pattern, which is passed in the \fIcode\fP argument. If the
1146  pattern has been studied, the result of the study should be passed in the  pattern was studied, the result of the study should be passed in the
1147  \fIextra\fP argument. This function is the main matching facility of the  \fIextra\fP argument. This function is the main matching facility of the
1148  library, and it operates in a Perl-like manner. For specialist use there is  library, and it operates in a Perl-like manner. For specialist use there is
1149  also an alternative matching function, which is described  also an alternative matching function, which is described
# Line 1186  the block by setting the other fields an Line 1211  the block by setting the other fields an
1211  The \fImatch_limit\fP field provides a means of preventing PCRE from using up a  The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
1212  vast amount of resources when running patterns that are not going to match,  vast amount of resources when running patterns that are not going to match,
1213  but which have a very large number of possibilities in their search trees. The  but which have a very large number of possibilities in their search trees. The
1214  classic example is the use of nested unlimited repeats.  classic example is a pattern that uses nested unlimited repeats.
1215  .P  .P
1216  Internally, PCRE uses a function called \fBmatch()\fP which it calls repeatedly  Internally, PCRE uses a function called \fBmatch()\fP which it calls repeatedly
1217  (sometimes recursively). The limit set by \fImatch_limit\fP is imposed on the  (sometimes recursively). The limit set by \fImatch_limit\fP is imposed on the
# Line 1246  documentation for a discussion of saving Line 1271  documentation for a discussion of saving
1271  .sp  .sp
1272  The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be  The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
1273  zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,  zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1274  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_START_OPTIMIZE,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
1275  PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_SOFT, and PCRE_PARTIAL_HARD.  PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_SOFT, and
1276    PCRE_PARTIAL_HARD.
1277  .sp  .sp
1278    PCRE_ANCHORED    PCRE_ANCHORED
1279  .sp  .sp
# Line 1322  match the empty string, the entire match Line 1348  match the empty string, the entire match
1348  .sp  .sp
1349    a?b?    a?b?
1350  .sp  .sp
1351  is applied to a string not beginning with "a" or "b", it matches the empty  is applied to a string not beginning with "a" or "b", it matches an empty
1352  string at the start of the subject. With PCRE_NOTEMPTY set, this match is not  string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1353  valid, so PCRE searches further into the string for occurrences of "a" or "b".  valid, so PCRE searches further into the string for occurrences of "a" or "b".
1354  .P  .sp
1355  Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case    PCRE_NOTEMPTY_ATSTART
1356  of a pattern match of the empty string within its \fBsplit()\fP function, and  .sp
1357  when using the /g modifier. It is possible to emulate Perl's behaviour after  This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1358  matching a null string by first trying the match again at the same offset with  the start of the subject is permitted. If the pattern is anchored, such a match
1359  PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the  can occur only if the pattern contains \eK.
1360  starting offset (see below) and trying an ordinary match again. There is some  .P
1361  code that demonstrates how to do this in the  Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1362    does make a special case of a pattern match of the empty string within its
1363    \fBsplit()\fP function, and when using the /g modifier. It is possible to
1364    emulate Perl's behaviour after matching a null string by first trying the match
1365    again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1366    if that fails, by advancing the starting offset (see below) and trying an
1367    ordinary match again. There is some code that demonstrates how to do this in
1368    the
1369  .\" HREF  .\" HREF
1370  \fBpcredemo\fP  \fBpcredemo\fP
1371  .\"  .\"
# Line 1477  the \fIovector\fP is not big enough to r Line 1510  the \fIovector\fP is not big enough to r
1510  has to get additional memory for use during matching. Thus it is usually  has to get additional memory for use during matching. Thus it is usually
1511  advisable to supply an \fIovector\fP.  advisable to supply an \fIovector\fP.
1512  .P  .P
1513  The \fBpcre_info()\fP function can be used to find out how many capturing  The \fBpcre_fullinfo()\fP function can be used to find out how many capturing
1514  subpatterns there are in a compiled pattern. The smallest size for  subpatterns there are in a compiled pattern. The smallest size for
1515  \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to  \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
1516  the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.  the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
# Line 1875  Here is an example of a simple call to \ Line 1908  Here is an example of a simple call to \
1908  .sp  .sp
1909  The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be  The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
1910  zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,  zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1911  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
1912  PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last  PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST,
1913  four of these are exactly the same as for \fBpcre_exec()\fP, so their  and PCRE_DFA_RESTART. All but the last four of these are exactly the same as
1914  description is not repeated here.  for \fBpcre_exec()\fP, so their description is not repeated here.
1915  .sp  .sp
1916    PCRE_PARTIAL_HARD    PCRE_PARTIAL_HARD
1917    PCRE_PARTIAL_SOFT    PCRE_PARTIAL_SOFT
# Line 2012  Cambridge CB2 3QH, England. Line 2045  Cambridge CB2 3QH, England.
2045  .rs  .rs
2046  .sp  .sp
2047  .nf  .nf
2048  Last updated: 09 September 2009  Last updated: 29 September 2009
2049  Copyright (c) 1997-2009 University of Cambridge.  Copyright (c) 1997-2009 University of Cambridge.
2050  .fi  .fi

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