doc/html/pcrepartial.html

<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>
</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> 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>. When this is done, the
return code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if at any
time during the matching process the entire subject string matched part of the
pattern. No captured data is set when this occurs.
</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 PCRE, the
PCRE_PARTIAL option cannot be used with all patterns. 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).
</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&#62; /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
  data&#62; 25jun04\P
   0: 25jun04
   1: jun
  data&#62; 25dec3\P
  Partial match
  data&#62; 3ju\P
  Partial match
  data&#62; 3juj\P
  No match
  data&#62; j\P
  No match
</pre>
The first data string is matched completely, so <b>pcretest</b> shows the
matched substrings. The remaining four strings do not match the complete
pattern, but the first two are partial matches.
</P>
<P>
Last updated: 08 September 2004
<br>
Copyright &copy; 1997-2004 University of Cambridge.
<p>
Return to the <a href="index.html">PCRE index page</a>.
</p>
1	<html>
2	<head>
3	<title>pcrepartial specification</title>
4	</head>
5	<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6	<h1>pcrepartial man page</h1>
7	<p>
8	Return to the <a href="index.html">PCRE index page</a>.
9	</p>
10	<p>
11	This page is part of the PCRE HTML documentation. It was generated automatically
12	from the original man page. If there is any nonsense in it, please consult the
13	man page, in case the conversion went wrong.
14	<br>
15	<ul>
16	<li><a name="TOC1" href="#SEC1">PARTIAL MATCHING IN PCRE</a>
17	<li><a name="TOC2" href="#SEC2">RESTRICTED PATTERNS FOR PCRE_PARTIAL</a>
18	<li><a name="TOC3" href="#SEC3">EXAMPLE OF PARTIAL MATCHING USING PCRETEST</a>
19	</ul>
20	<br><a name="SEC1" href="#TOC1">PARTIAL MATCHING IN PCRE</a><br>
21	<P>
22	In normal use of PCRE, if the subject string that is passed to
23	<b>pcre_exec()</b> matches as far as it goes, but is too short to match the
24	entire pattern, PCRE_ERROR_NOMATCH is returned. There are circumstances where
25	it might be helpful to distinguish this case from other cases in which there is
26	no match.
27	</P>
28	<P>
29	Consider, for example, an application where a human is required to type in data
30	for a field with specific formatting requirements. An example might be a date
31	in the form <i>ddmmmyy</i>, defined by this pattern:
32	<pre>
33	^\d?\d(jan\|feb\|mar\|apr\|may\|jun\|jul\|aug\|sep\|oct\|nov\|dec)\d\d$
34	</pre>
35	If the application sees the user's keystrokes one by one, and can check that
36	what has been typed so far is potentially valid, it is able to raise an error
37	as soon as a mistake is made, possibly beeping and not reflecting the
38	character that has been typed. This immediate feedback is likely to be a better
39	user interface than a check that is delayed until the entire string has been
40	entered.
41	</P>
42	<P>
43	PCRE supports the concept of partial matching by means of the PCRE_PARTIAL
44	option, which can be set when calling <b>pcre_exec()</b>. When this is done, the
45	return code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if at any
46	time during the matching process the entire subject string matched part of the
47	pattern. No captured data is set when this occurs.
48	</P>
49	<P>
50	Using PCRE_PARTIAL disables one of PCRE's optimizations. PCRE remembers the
51	last literal byte in a pattern, and abandons matching immediately if such a
52	byte is not present in the subject string. This optimization cannot be used
53	for a subject string that might match only partially.
54	</P>
55	<br><a name="SEC2" href="#TOC1">RESTRICTED PATTERNS FOR PCRE_PARTIAL</a><br>
56	<P>
57	Because of the way certain internal optimizations are implemented in PCRE, the
58	PCRE_PARTIAL option cannot be used with all patterns. Repeated single
59	characters such as
60	<pre>
61	a{2,4}
62	</pre>
63	and repeated single metasequences such as
64	<pre>
65	\d+
66	</pre>
67	are not permitted if the maximum number of occurrences is greater than one.
68	Optional items such as \d? (where the maximum is one) are permitted.
69	Quantifiers with any values are permitted after parentheses, so the invalid
70	examples above can be coded thus:
71	<pre>
72	(a){2,4}
73	(\d)+
74	</pre>
75	These constructions run more slowly, but for the kinds of application that are
76	envisaged for this facility, this is not felt to be a major restriction.
77	</P>
78	<P>
79	If PCRE_PARTIAL is set for a pattern that does not conform to the restrictions,
80	<b>pcre_exec()</b> returns the error code PCRE_ERROR_BADPARTIAL (-13).
81	</P>
82	<br><a name="SEC3" href="#TOC1">EXAMPLE OF PARTIAL MATCHING USING PCRETEST</a><br>
83	<P>
84	If the escape sequence \P is present in a <b>pcretest</b> data line, the
85	PCRE_PARTIAL flag is used for the match. Here is a run of <b>pcretest</b> that
86	uses the date example quoted above:
87	<pre>
88	re> /^\d?\d(jan\|feb\|mar\|apr\|may\|jun\|jul\|aug\|sep\|oct\|nov\|dec)\d\d$/
89	data> 25jun04\P
90	0: 25jun04
91	1: jun
92	data> 25dec3\P
93	Partial match
94	data> 3ju\P
95	Partial match
96	data> 3juj\P
97	No match
98	data> j\P
99	No match
100	</pre>
101	The first data string is matched completely, so <b>pcretest</b> shows the
102	matched substrings. The remaining four strings do not match the complete
103	pattern, but the first two are partial matches.
104	</P>
105	<P>
106	Last updated: 08 September 2004
107	<br>
108	Copyright © 1997-2004 University of Cambridge.
109	<p>
110	Return to the <a href="index.html">PCRE index page</a>.
111	</p>