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version 1.1.1.4, 2013/07/22 08:25:56
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Line 6 PCRE - Perl-compatible regular expressions
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Line 6 PCRE - Perl-compatible regular expressions
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This document describes the two different algorithms that are available in PCRE |
This document describes the two different algorithms that are available in PCRE |
for matching a compiled regular expression against a given subject string. The |
for matching a compiled regular expression against a given subject string. The |
"standard" algorithm is the one provided by the \fBpcre_exec()\fP and | "standard" algorithm is the one provided by the \fBpcre_exec()\fP, |
\fBpcre16_exec()\fP functions. These work in the same was as Perl's matching | \fBpcre16_exec()\fP and \fBpcre32_exec()\fP functions. These work in the same |
function, and provide a Perl-compatible matching operation. The just-in-time | as as Perl's matching function, and provide a Perl-compatible matching operation. |
(JIT) optimization that is described in the | The just-in-time (JIT) optimization that is described in the |
.\" HREF |
.\" HREF |
\fBpcrejit\fP |
\fBpcrejit\fP |
.\" |
.\" |
documentation is compatible with these functions. |
documentation is compatible with these functions. |
.P |
.P |
An alternative algorithm is provided by the \fBpcre_dfa_exec()\fP and | An alternative algorithm is provided by the \fBpcre_dfa_exec()\fP, |
\fBpcre16_dfa_exec()\fP functions; they operate in a different way, and are not | \fBpcre16_dfa_exec()\fP and \fBpcre32_dfa_exec()\fP functions; they operate in |
Perl-compatible. This alternative has advantages and disadvantages compared | a different way, and are not Perl-compatible. This alternative has advantages |
with the standard algorithm, and these are described below. | and disadvantages compared with the standard algorithm, and these are described |
| below. |
.P |
.P |
When there is only one possible way in which a given subject string can match a |
When there is only one possible way in which a given subject string can match a |
pattern, the two algorithms give the same answer. A difference arises, however, |
pattern, the two algorithms give the same answer. A difference arises, however, |
Line 140 and not on others), is not supported. It causes an err
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Line 141 and not on others), is not supported. It causes an err
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always 1, and the value of the \fIcapture_last\fP field is always -1. |
always 1, and the value of the \fIcapture_last\fP field is always -1. |
.P |
.P |
7. The \eC escape sequence, which (in the standard algorithm) always matches a |
7. The \eC escape sequence, which (in the standard algorithm) always matches a |
single data unit, even in UTF-8 or UTF-16 modes, is not supported in these | single data unit, even in UTF-8, UTF-16 or UTF-32 modes, is not supported in |
modes, because the alternative algorithm moves through the subject string one | these modes, because the alternative algorithm moves through the subject string |
character (not data unit) at a time, for all active paths through the tree. | one character (not data unit) at a time, for all active paths through the tree. |
.P |
.P |
8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) are not |
8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) are not |
supported. (*FAIL) is supported, and behaves like a failing negative assertion. |
supported. (*FAIL) is supported, and behaves like a failing negative assertion. |