/[pcre]/code/trunk/doc/pcreapi.3
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revision 548 by ph10, Fri Jun 25 14:42:00 2010 UTC revision 568 by ph10, Sat Nov 6 17:36:26 2010 UTC
# Line 1450  the Line 1450  the
1450  .\" HREF  .\" HREF
1451  \fBpcredemo\fP  \fBpcredemo\fP
1452  .\"  .\"
1453  sample program.  sample program. In the most general case, you have to check to see if the
1454    newline convention recognizes CRLF as a newline, and if so, and the current
1455    character is CR followed by LF, advance the starting offset by two characters
1456    instead of one.
1457  .sp  .sp
1458    PCRE_NO_START_OPTIMIZE    PCRE_NO_START_OPTIMIZE
1459  .sp  .sp
# Line 1512  in the main Line 1515  in the main
1515  \fBpcre\fP  \fBpcre\fP
1516  .\"  .\"
1517  page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_exec()\fP returns  page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_exec()\fP returns
1518  the error PCRE_ERROR_BADUTF8. If \fIstartoffset\fP contains an invalid value,  the error PCRE_ERROR_BADUTF8. If \fIstartoffset\fP contains a value that does
1519    not point to the start of a UTF-8 character (or to the end of the subject),
1520  PCRE_ERROR_BADUTF8_OFFSET is returned.  PCRE_ERROR_BADUTF8_OFFSET is returned.
1521  .P  .P
1522  If you already know that your subject is valid, and you want to skip these  If you already know that your subject is valid, and you want to skip these
# Line 1520  checks for performance reasons, you can Line 1524  checks for performance reasons, you can
1524  calling \fBpcre_exec()\fP. You might want to do this for the second and  calling \fBpcre_exec()\fP. You might want to do this for the second and
1525  subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find  subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
1526  all the matches in a single subject string. However, you should be sure that  all the matches in a single subject string. However, you should be sure that
1527  the value of \fIstartoffset\fP points to the start of a UTF-8 character. When  the value of \fIstartoffset\fP points to the start of a UTF-8 character (or the
1528  PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a  end of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
1529  subject, or a value of \fIstartoffset\fP that does not point to the start of a  invalid UTF-8 string as a subject or an invalid value of \fIstartoffset\fP is
1530  UTF-8 character, is undefined. Your program may crash.  undefined. Your program may crash.
1531  .sp  .sp
1532    PCRE_PARTIAL_HARD    PCRE_PARTIAL_HARD
1533    PCRE_PARTIAL_SOFT    PCRE_PARTIAL_SOFT
# Line 1532  These options turn on the partial matchi Line 1536  These options turn on the partial matchi
1536  compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match  compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1537  occurs if the end of the subject string is reached successfully, but there are  occurs if the end of the subject string is reached successfully, but there are
1538  not enough subject characters to complete the match. If this happens when  not enough subject characters to complete the match. If this happens when
1539  PCRE_PARTIAL_HARD is set, \fBpcre_exec()\fP immediately returns  PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
1540  PCRE_ERROR_PARTIAL. Otherwise, if PCRE_PARTIAL_SOFT is set, matching continues  testing any remaining alternatives. Only if no complete match can be found is
1541  by testing any other alternatives. Only if they all fail is PCRE_ERROR_PARTIAL  PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
1542  returned (instead of PCRE_ERROR_NOMATCH). The portion of the string that  PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
1543  was inspected when the partial match was found is set as the first matching  but only if no complete match can be found.
1544  string. There is a more detailed discussion in the  .P
1545    If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
1546    partial match is found, \fBpcre_exec()\fP immediately returns
1547    PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
1548    when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
1549    important that an alternative complete match.
1550    .P
1551    In both cases, the portion of the string that was inspected when the partial
1552    match was found is set as the first matching string. There is a more detailed
1553    discussion of partial and multi-segment matching, with examples, in the
1554  .\" HREF  .\" HREF
1555  \fBpcrepartial\fP  \fBpcrepartial\fP
1556  .\"  .\"
1557  documentation.  documentation.
1558  .  .
1559    .
1560  .SS "The string to be matched by \fBpcre_exec()\fP"  .SS "The string to be matched by \fBpcre_exec()\fP"
1561  .rs  .rs
1562  .sp  .sp
1563  The subject string is passed to \fBpcre_exec()\fP as a pointer in  The subject string is passed to \fBpcre_exec()\fP as a pointer in
1564  \fIsubject\fP, a length (in bytes) in \fIlength\fP, and a starting byte offset  \fIsubject\fP, a length (in bytes) in \fIlength\fP, and a starting byte offset
1565  in \fIstartoffset\fP. In UTF-8 mode, the byte offset must point to the start of  in \fIstartoffset\fP. If this is negative or greater than the length of the
1566  a UTF-8 character. Unlike the pattern string, the subject may contain binary  subject, \fBpcre_exec()\fP returns PCRE_ERROR_BADOFFSET.
1567  zero bytes. When the starting offset is zero, the search for a match starts at  .P
1568  the beginning of the subject, and this is by far the most common case.  In UTF-8 mode, the byte offset must point to the start of a UTF-8 character (or
1569    the end of the subject). Unlike the pattern string, the subject may contain
1570    binary zero bytes. When the starting offset is zero, the search for a match
1571    starts at the beginning of the subject, and this is by far the most common
1572    case.
1573  .P  .P
1574  A non-zero starting offset is useful when searching for another match in the  A non-zero starting offset is useful when searching for another match in the
1575  same subject by calling \fBpcre_exec()\fP again after a previous success.  same subject by calling \fBpcre_exec()\fP again after a previous success.
# Line 1571  start of the subject, which is deemed to Line 1589  start of the subject, which is deemed to
1589  set to 4, it finds the second occurrence of "iss" because it is able to look  set to 4, it finds the second occurrence of "iss" because it is able to look
1590  behind the starting point to discover that it is preceded by a letter.  behind the starting point to discover that it is preceded by a letter.
1591  .P  .P
1592    Finding all the matches in a subject is tricky when the pattern can match an
1593    empty string. It is possible to emulate Perl's /g behaviour by first trying the
1594    match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
1595    PCRE_ANCHORED options, and then if that fails, advancing the starting offset
1596    and trying an ordinary match again. There is some code that demonstrates how to
1597    do this in the
1598    .\" HREF
1599    \fBpcredemo\fP
1600    .\"
1601    sample program. In the most general case, you have to check to see if the
1602    newline convention recognizes CRLF as a newline, and if so, and the current
1603    character is CR followed by LF, advance the starting offset by two characters
1604    instead of one.
1605    .P
1606  If a non-zero starting offset is passed when the pattern is anchored, one  If a non-zero starting offset is passed when the pattern is anchored, one
1607  attempt to match at the given offset is made. This can only succeed if the  attempt to match at the given offset is made. This can only succeed if the
1608  pattern does not require the match to be at the start of the subject.  pattern does not require the match to be at the start of the subject.
1609  .  .
1610    .
1611  .SS "How \fBpcre_exec()\fP returns captured substrings"  .SS "How \fBpcre_exec()\fP returns captured substrings"
1612  .rs  .rs
1613  .sp  .sp
# Line 1641  Offset values that correspond to unused Line 1674  Offset values that correspond to unused
1674  expression are also set to -1. For example, if the string "abc" is matched  expression are also set to -1. For example, if the string "abc" is matched
1675  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1676  return from the function is 2, because the highest used capturing subpattern  return from the function is 2, because the highest used capturing subpattern
1677  number is 1. However, you can refer to the offsets for the second and third  number is 1, and the offsets for for the second and third capturing subpatterns
1678  capturing subpatterns if you wish (assuming the vector is large enough, of  (assuming the vector is large enough, of course) are set to -1.
1679  course).  .P
1680    \fBNote\fP: Elements of \fIovector\fP that do not correspond to capturing
1681    parentheses in the pattern are never changed. That is, if a pattern contains
1682    \fIn\fP capturing parentheses, no more than \fIovector[0]\fP to
1683    \fIovector[2n+1]\fP are set by \fBpcre_exec()\fP. The other elements retain
1684    whatever values they previously had.
1685  .P  .P
1686  Some convenience functions are provided for extracting the captured substrings  Some convenience functions are provided for extracting the captured substrings
1687  as separate strings. These are described below.  as separate strings. These are described below.
# Line 1757  description above. Line 1795  description above.
1795    PCRE_ERROR_BADNEWLINE     (-23)    PCRE_ERROR_BADNEWLINE     (-23)
1796  .sp  .sp
1797  An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.  An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
1798    .sp
1799      PCRE_ERROR_BADOFFSET      (-24)
1800    .sp
1801    The value of \fIstartoffset\fP was negative or greater than the length of the
1802    subject, that is, the value in \fIlength\fP.
1803  .P  .P
1804  Error numbers -16 to -20 and -22 are not used by \fBpcre_exec()\fP.  Error numbers -16 to -20 and -22 are not used by \fBpcre_exec()\fP.
1805  .  .
# Line 2059  is converted into PCRE_ERROR_PARTIAL if Line 2102  is converted into PCRE_ERROR_PARTIAL if
2102  there have been no complete matches, but there is still at least one matching  there have been no complete matches, but there is still at least one matching
2103  possibility. The portion of the string that was inspected when the longest  possibility. The portion of the string that was inspected when the longest
2104  partial match was found is set as the first matching string in both cases.  partial match was found is set as the first matching string in both cases.
2105    There is a more detailed discussion of partial and multi-segment matching, with
2106    examples, in the
2107    .\" HREF
2108    \fBpcrepartial\fP
2109    .\"
2110    documentation.
2111  .sp  .sp
2112    PCRE_DFA_SHORTEST    PCRE_DFA_SHORTEST
2113  .sp  .sp
# Line 2178  Cambridge CB2 3QH, England. Line 2227  Cambridge CB2 3QH, England.
2227  .rs  .rs
2228  .sp  .sp
2229  .nf  .nf
2230  Last updated: 21 June 2010  Last updated: 06 November 2010
2231  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2010 University of Cambridge.
2232  .fi  .fi

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