/[pcre]/code/trunk/doc/pcreapi.3
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revision 545 by ph10, Wed Jun 16 10:51:15 2010 UTC revision 546 by ph10, Sun Jun 20 15:44:12 2010 UTC
# Line 765  out of use. To avoid confusion, they hav Line 765  out of use. To avoid confusion, they hav
765    50  [this code is not in use]    50  [this code is not in use]
766    51  octal value is greater than \e377 (not in UTF-8 mode)    51  octal value is greater than \e377 (not in UTF-8 mode)
767    52  internal error: overran compiling workspace    52  internal error: overran compiling workspace
768    53  internal error: previously-checked referenced subpattern not found    53  internal error: previously-checked referenced subpattern
769            not found
770    54  DEFINE group contains more than one branch    54  DEFINE group contains more than one branch
771    55  repeating a DEFINE group is not allowed    55  repeating a DEFINE group is not allowed
772    56  inconsistent NEWLINE options    56  inconsistent NEWLINE options
# Line 778  out of use. To avoid confusion, they hav Line 779  out of use. To avoid confusion, they hav
779    62  subpattern name expected    62  subpattern name expected
780    63  digit expected after (?+    63  digit expected after (?+
781    64  ] is an invalid data character in JavaScript compatibility mode    64  ] is an invalid data character in JavaScript compatibility mode
782    65  different names for subpatterns of the same number are not allowed    65  different names for subpatterns of the same number are
783            not allowed
784    66  (*MARK) must have an argument    66  (*MARK) must have an argument
785    67  this version of PCRE is not compiled with PCRE_UCP support    67  this version of PCRE is not compiled with PCRE_UCP support
786  .sp  .sp
# Line 1448  unanchored match must start with a speci Line 1450  unanchored match must start with a speci
1450  for that character, and fails immediately if it cannot find it, without  for that character, and fails immediately if it cannot find it, without
1451  actually running the main matching function. This means that a special item  actually running the main matching function. This means that a special item
1452  such as (*COMMIT) at the start of a pattern is not considered until after a  such as (*COMMIT) at the start of a pattern is not considered until after a
1453  suitable starting point for the match has been found. When callouts are in use,  suitable starting point for the match has been found. When callouts or (*MARK)
1454  these "start-up" optimizations can cause them to be skipped if the pattern is  items are in use, these "start-up" optimizations can cause them to be skipped
1455  never actually used. The PCRE_NO_START_OPTIMIZE option disables the start-up  if the pattern is never actually used. The start-up optimizations are in effect
1456  optimizations, causing performance to suffer, but ensuring that the callouts do  a pre-scan of the subject that takes place before the pattern is run.
1457  occur, and that items such as (*COMMIT) are considered at every possible  .P
1458  starting position in the subject string.  The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1459    causing performance to suffer, but ensuring that in cases where the result is
1460    "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1461    are considered at every possible starting position in the subject string.
1462    Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1463    Consider the pattern
1464    .sp
1465      (*COMMIT)ABC
1466    .sp
1467    When this is compiled, PCRE records the fact that a match must start with the
1468    character "A". Suppose the subject string is "DEFABC". The start-up
1469    optimization scans along the subject, finds "A" and runs the first match
1470    attempt from there. The (*COMMIT) item means that the pattern must match the
1471    current starting position, which in this case, it does. However, if the same
1472    match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1473    subject string does not happen. The first match attempt is run starting from
1474    "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1475    the overall result is "no match". If the pattern is studied, more start-up
1476    optimizations may be used. For example, a minimum length for the subject may be
1477    recorded. Consider the pattern
1478    .sp
1479      (*MARK:A)(X|Y)
1480    .sp
1481    The minimum length for a match is one character. If the subject is "ABC", there
1482    will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1483    If the pattern is studied, the final attempt does not take place, because PCRE
1484    knows that the subject is too short, and so the (*MARK) is never encountered.
1485    In this case, studying the pattern does not affect the overall match result,
1486    which is still "no match", but it does affect the auxiliary information that is
1487    returned.
1488  .sp  .sp
1489    PCRE_NO_UTF8_CHECK    PCRE_NO_UTF8_CHECK
1490  .sp  .sp
# Line 2137  Cambridge CB2 3QH, England. Line 2168  Cambridge CB2 3QH, England.
2168  .rs  .rs
2169  .sp  .sp
2170  .nf  .nf
2171  Last updated: 15 June 2010  Last updated: 20 June 2010
2172  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2010 University of Cambridge.
2173  .fi  .fi

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