/[pcre]/code/trunk/doc/pcreapi.3
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revision 566 by ph10, Wed Nov 3 18:32:55 2010 UTC revision 568 by ph10, Sat Nov 6 17:36:26 2010 UTC
# Line 1515  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 1523  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 1555  discussion of partial and multi-segment Line 1556  discussion of partial and multi-segment
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 1583  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 1653  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 1769  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 2196  Cambridge CB2 3QH, England. Line 2227  Cambridge CB2 3QH, England.
2227  .rs  .rs
2228  .sp  .sp
2229  .nf  .nf
2230  Last updated: 01 November 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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