--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/libraries/spcre/libpcre/pcre/doc/html/pcrepartial.html Wed Jun 23 15:52:26 2010 +0100
@@ -0,0 +1,242 @@
+<html>
+<head>
+<title>pcrepartial specification</title>
+</head>
+<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
+<h1>pcrepartial man page</h1>
+<p>
+Return to the <a href="index.html">PCRE index page</a>.
+</p>
+<p>
+This page is part of the PCRE HTML documentation. It was generated automatically
+from the original man page. If there is any nonsense in it, please consult the
+man page, in case the conversion went wrong.
+<br>
+<ul>
+<li><a name="TOC1" href="#SEC1">PARTIAL MATCHING IN PCRE</a>
+<li><a name="TOC2" href="#SEC2">RESTRICTED PATTERNS FOR PCRE_PARTIAL</a>
+<li><a name="TOC3" href="#SEC3">EXAMPLE OF PARTIAL MATCHING USING PCRETEST</a>
+<li><a name="TOC4" href="#SEC4">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()</a>
+<li><a name="TOC5" href="#SEC5">AUTHOR</a>
+<li><a name="TOC6" href="#SEC6">REVISION</a>
+</ul>
+<br><a name="SEC1" href="#TOC1">PARTIAL MATCHING IN PCRE</a><br>
+<P>
+In normal use of PCRE, if the subject string that is passed to
+<b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> matches as far as it goes, but is
+too short to match the entire pattern, PCRE_ERROR_NOMATCH is returned. There
+are circumstances where it might be helpful to distinguish this case from other
+cases in which there is no match.
+</P>
+<P>
+Consider, for example, an application where a human is required to type in data
+for a field with specific formatting requirements. An example might be a date
+in the form <i>ddmmmyy</i>, defined by this pattern:
+<pre>
+ ^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$
+</pre>
+If the application sees the user's keystrokes one by one, and can check that
+what has been typed so far is potentially valid, it is able to raise an error
+as soon as a mistake is made, possibly beeping and not reflecting the
+character that has been typed. This immediate feedback is likely to be a better
+user interface than a check that is delayed until the entire string has been
+entered.
+</P>
+<P>
+PCRE supports the concept of partial matching by means of the PCRE_PARTIAL
+option, which can be set when calling <b>pcre_exec()</b> or
+<b>pcre_dfa_exec()</b>. When this flag is set for <b>pcre_exec()</b>, the return
+code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if at any time
+during the matching process the last part of the subject string matched part of
+the pattern. Unfortunately, for non-anchored matching, it is not possible to
+obtain the position of the start of the partial match. No captured data is set
+when PCRE_ERROR_PARTIAL is returned.
+</P>
+<P>
+When PCRE_PARTIAL is set for <b>pcre_dfa_exec()</b>, the return code
+PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end of the
+subject is reached, there have been no complete matches, but there is still at
+least one matching possibility. The portion of the string that provided the
+partial match is set as the first matching string.
+</P>
+<P>
+Using PCRE_PARTIAL disables one of PCRE's optimizations. PCRE remembers the
+last literal byte in a pattern, and abandons matching immediately if such a
+byte is not present in the subject string. This optimization cannot be used
+for a subject string that might match only partially.
+</P>
+<br><a name="SEC2" href="#TOC1">RESTRICTED PATTERNS FOR PCRE_PARTIAL</a><br>
+<P>
+Because of the way certain internal optimizations are implemented in the
+<b>pcre_exec()</b> function, the PCRE_PARTIAL option cannot be used with all
+patterns. These restrictions do not apply when <b>pcre_dfa_exec()</b> is used.
+For <b>pcre_exec()</b>, repeated single characters such as
+<pre>
+ a{2,4}
+</pre>
+and repeated single metasequences such as
+<pre>
+ \d+
+</pre>
+are not permitted if the maximum number of occurrences is greater than one.
+Optional items such as \d? (where the maximum is one) are permitted.
+Quantifiers with any values are permitted after parentheses, so the invalid
+examples above can be coded thus:
+<pre>
+ (a){2,4}
+ (\d)+
+</pre>
+These constructions run more slowly, but for the kinds of application that are
+envisaged for this facility, this is not felt to be a major restriction.
+</P>
+<P>
+If PCRE_PARTIAL is set for a pattern that does not conform to the restrictions,
+<b>pcre_exec()</b> returns the error code PCRE_ERROR_BADPARTIAL (-13).
+You can use the PCRE_INFO_OKPARTIAL call to <b>pcre_fullinfo()</b> to find out
+if a compiled pattern can be used for partial matching.
+</P>
+<br><a name="SEC3" href="#TOC1">EXAMPLE OF PARTIAL MATCHING USING PCRETEST</a><br>
+<P>
+If the escape sequence \P is present in a <b>pcretest</b> data line, the
+PCRE_PARTIAL flag is used for the match. Here is a run of <b>pcretest</b> that
+uses the date example quoted above:
+<pre>
+ re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
+ data> 25jun04\P
+ 0: 25jun04
+ 1: jun
+ data> 25dec3\P
+ Partial match
+ data> 3ju\P
+ Partial match
+ data> 3juj\P
+ No match
+ data> j\P
+ No match
+</pre>
+The first data string is matched completely, so <b>pcretest</b> shows the
+matched substrings. The remaining four strings do not match the complete
+pattern, but the first two are partial matches. The same test, using
+<b>pcre_dfa_exec()</b> matching (by means of the \D escape sequence), produces
+the following output:
+<pre>
+ re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
+ data> 25jun04\P\D
+ 0: 25jun04
+ data> 23dec3\P\D
+ Partial match: 23dec3
+ data> 3ju\P\D
+ Partial match: 3ju
+ data> 3juj\P\D
+ No match
+ data> j\P\D
+ No match
+</pre>
+Notice that in this case the portion of the string that was matched is made
+available.
+</P>
+<br><a name="SEC4" href="#TOC1">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()</a><br>
+<P>
+When a partial match has been found using <b>pcre_dfa_exec()</b>, it is possible
+to continue the match by providing additional subject data and calling
+<b>pcre_dfa_exec()</b> again with the same compiled regular expression, this
+time setting the PCRE_DFA_RESTART option. You must also pass the same working
+space as before, because this is where details of the previous partial match
+are stored. Here is an example using <b>pcretest</b>, using the \R escape
+sequence to set the PCRE_DFA_RESTART option (\P and \D are as above):
+<pre>
+ re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
+ data> 23ja\P\D
+ Partial match: 23ja
+ data> n05\R\D
+ 0: n05
+</pre>
+The first call has "23ja" as the subject, and requests partial matching; the
+second call has "n05" as the subject for the continued (restarted) match.
+Notice that when the match is complete, only the last part is shown; PCRE does
+not retain the previously partially-matched string. It is up to the calling
+program to do that if it needs to.
+</P>
+<P>
+You can set PCRE_PARTIAL with PCRE_DFA_RESTART to continue partial matching
+over multiple segments. This facility can be used to pass very long subject
+strings to <b>pcre_dfa_exec()</b>. However, some care is needed for certain
+types of pattern.
+</P>
+<P>
+1. If the pattern contains tests for the beginning or end of a line, you need
+to pass the PCRE_NOTBOL or PCRE_NOTEOL options, as appropriate, when the
+subject string for any call does not contain the beginning or end of a line.
+</P>
+<P>
+2. If the pattern contains backward assertions (including \b or \B), you need
+to arrange for some overlap in the subject strings to allow for this. For
+example, you could pass the subject in chunks that are 500 bytes long, but in
+a buffer of 700 bytes, with the starting offset set to 200 and the previous 200
+bytes at the start of the buffer.
+</P>
+<P>
+3. Matching a subject string that is split into multiple segments does not
+always produce exactly the same result as matching over one single long string.
+The difference arises when there are multiple matching possibilities, because a
+partial match result is given only when there are no completed matches in a
+call to <b>pcre_dfa_exec()</b>. This means that as soon as the shortest match has
+been found, continuation to a new subject segment is no longer possible.
+Consider this <b>pcretest</b> example:
+<pre>
+ re> /dog(sbody)?/
+ data> do\P\D
+ Partial match: do
+ data> gsb\R\P\D
+ 0: g
+ data> dogsbody\D
+ 0: dogsbody
+ 1: dog
+</pre>
+The pattern matches the words "dog" or "dogsbody". When the subject is
+presented in several parts ("do" and "gsb" being the first two) the match stops
+when "dog" has been found, and it is not possible to continue. On the other
+hand, if "dogsbody" is presented as a single string, both matches are found.
+</P>
+<P>
+Because of this phenomenon, it does not usually make sense to end a pattern
+that is going to be matched in this way with a variable repeat.
+</P>
+<P>
+4. Patterns that contain alternatives at the top level which do not all
+start with the same pattern item may not work as expected. For example,
+consider this pattern:
+<pre>
+ 1234|3789
+</pre>
+If the first part of the subject is "ABC123", a partial match of the first
+alternative is found at offset 3. There is no partial match for the second
+alternative, because such a match does not start at the same point in the
+subject string. Attempting to continue with the string "789" does not yield a
+match because only those alternatives that match at one point in the subject
+are remembered. The problem arises because the start of the second alternative
+matches within the first alternative. There is no problem with anchored
+patterns or patterns such as:
+<pre>
+ 1234|ABCD
+</pre>
+where no string can be a partial match for both alternatives.
+</P>
+<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
+<P>
+Philip Hazel
+<br>
+University Computing Service
+<br>
+Cambridge CB2 3QH, England.
+<br>
+</P>
+<br><a name="SEC6" href="#TOC1">REVISION</a><br>
+<P>
+Last updated: 04 June 2007
+<br>
+Copyright © 1997-2007 University of Cambridge.
+<br>
+<p>
+Return to the <a href="index.html">PCRE index page</a>.
+</p>