doc/html/pcreprecompile.html

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<title>pcreprecompile specification</title>
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<h1>pcreprecompile 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">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a>
<li><a name="TOC2" href="#SEC2">SAVING A COMPILED PATTERN</a>
<li><a name="TOC3" href="#SEC3">RE-USING A PRECOMPILED PATTERN</a>
<li><a name="TOC4" href="#SEC4">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a>
<li><a name="TOC5" href="#SEC5">AUTHOR</a>
<li><a name="TOC6" href="#SEC6">REVISION</a>
</ul>
<br><a name="SEC1" href="#TOC1">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a><br>
<P>
If you are running an application that uses a large number of regular
expression patterns, it may be useful to store them in a precompiled form
instead of having to compile them every time the application is run.
If you are not using any private character tables (see the
<a href="pcre_maketables.html"><b>pcre_maketables()</b></a>
documentation), this is relatively straightforward. If you are using private
tables, it is a little bit more complicated. However, if you are using the
just-in-time optimization feature, it is not possible to save and reload the
JIT data.
</P>
<P>
If you save compiled patterns to a file, you can copy them to a different host
and run them there. If the two hosts have different endianness (byte order),
you should run the <b>pcre[16|32]_pattern_to_host_byte_order()</b> function on the
new host before trying to match the pattern. The matching functions return
PCRE_ERROR_BADENDIANNESS if they detect a pattern with the wrong endianness.
</P>
<P>
Compiling regular expressions with one version of PCRE for use with a different
version is not guaranteed to work and may cause crashes, and saving and
restoring a compiled pattern loses any JIT optimization data.
</P>
<br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
<P>
The value returned by <b>pcre[16|32]_compile()</b> points to a single block of
memory that holds the compiled pattern and associated data. You can find the
length of this block in bytes by calling <b>pcre[16|32]_fullinfo()</b> with an
argument of PCRE_INFO_SIZE. You can then save the data in any appropriate
manner. Here is sample code for the 8-bit library that compiles a pattern and
writes it to a file. It assumes that the variable <i>fd</i> refers to a file
that is open for output:
<pre>
  int erroroffset, rc, size;
  char *error;
  pcre *re;

  re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
  if (re == NULL) { ... handle errors ... }
  rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
  if (rc &#60; 0) { ... handle errors ... }
  rc = fwrite(re, 1, size, fd);
  if (rc != size) { ... handle errors ... }
</pre>
In this example, the bytes that comprise the compiled pattern are copied
exactly. Note that this is binary data that may contain any of the 256 possible
byte values. On systems that make a distinction between binary and non-binary
data, be sure that the file is opened for binary output.
</P>
<P>
If you want to write more than one pattern to a file, you will have to devise a
way of separating them. For binary data, preceding each pattern with its length
is probably the most straightforward approach. Another possibility is to write
out the data in hexadecimal instead of binary, one pattern to a line.
</P>
<P>
Saving compiled patterns in a file is only one possible way of storing them for
later use. They could equally well be saved in a database, or in the memory of
some daemon process that passes them via sockets to the processes that want
them.
</P>
<P>
If the pattern has been studied, it is also possible to save the normal study
data in a similar way to the compiled pattern itself. However, if the
PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is created cannot
be saved because it is too dependent on the current environment. When studying
generates additional information, <b>pcre[16|32]_study()</b> returns a pointer to a
<b>pcre[16|32]_extra</b> data block. Its format is defined in the
<a href="pcreapi.html#extradata">section on matching a pattern</a>
in the
<a href="pcreapi.html"><b>pcreapi</b></a>
documentation. The <i>study_data</i> field points to the binary study data, and
this is what you must save (not the <b>pcre[16|32]_extra</b> block itself). The
length of the study data can be obtained by calling <b>pcre[16|32]_fullinfo()</b>
with an argument of PCRE_INFO_STUDYSIZE. Remember to check that
<b>pcre[16|32]_study()</b> did return a non-NULL value before trying to save the
study data.
</P>
<br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
<P>
Re-using a precompiled pattern is straightforward. Having reloaded it into main
memory, called <b>pcre[16|32]_pattern_to_host_byte_order()</b> if necessary,
you pass its pointer to <b>pcre[16|32]_exec()</b> or <b>pcre[16|32]_dfa_exec()</b> in
the usual way.
</P>
<P>
However, if you passed a pointer to custom character tables when the pattern
was compiled (the <i>tableptr</i> argument of <b>pcre[16|32]_compile()</b>), you
must now pass a similar pointer to <b>pcre[16|32]_exec()</b> or
<b>pcre[16|32]_dfa_exec()</b>, because the value saved with the compiled pattern
will obviously be nonsense. A field in a <b>pcre[16|32]_extra()</b> block is used
to pass this data, as described in the
<a href="pcreapi.html#extradata">section on matching a pattern</a>
in the
<a href="pcreapi.html"><b>pcreapi</b></a>
documentation.
</P>
<P>
If you did not provide custom character tables when the pattern was compiled,
the pointer in the compiled pattern is NULL, which causes the matching
functions to use PCRE's internal tables. Thus, you do not need to take any
special action at run time in this case.
</P>
<P>
If you saved study data with the compiled pattern, you need to create your own
<b>pcre[16|32]_extra</b> data block and set the <i>study_data</i> field to point to the
reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
<i>flags</i> field to indicate that study data is present. Then pass the
<b>pcre[16|32]_extra</b> block to the matching function in the usual way. If the
pattern was studied for just-in-time optimization, that data cannot be saved,
and so is lost by a save/restore cycle.
</P>
<br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
<P>
In general, it is safest to recompile all saved patterns when you update to a
new PCRE release, though not all updates actually require this.
</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: 24 June 2012
<br>
Copyright &copy; 1997-2012 University of Cambridge.
<br>
<p>
Return to the <a href="index.html">PCRE index page</a>.
</p>
1	nigel	75	<html>
2			<head>
3			<title>pcreprecompile specification</title>
4			</head>
5			<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6			<h1>pcreprecompile man page</h1>
7			<p>
8			Return to the <a href="index.html">PCRE index page</a>.
9			</p>
10	ph10	111	<p>
11	nigel	75	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	ph10	111	<br>
15	nigel	75	<ul>
16			<li><a name="TOC1" href="#SEC1">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a>
17			<li><a name="TOC2" href="#SEC2">SAVING A COMPILED PATTERN</a>
18			<li><a name="TOC3" href="#SEC3">RE-USING A PRECOMPILED PATTERN</a>
19			<li><a name="TOC4" href="#SEC4">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a>
20	ph10	99	<li><a name="TOC5" href="#SEC5">AUTHOR</a>
21			<li><a name="TOC6" href="#SEC6">REVISION</a>
22	nigel	75	</ul>
23			<br><a name="SEC1" href="#TOC1">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a><br>
24			<P>
25			If you are running an application that uses a large number of regular
26			expression patterns, it may be useful to store them in a precompiled form
27			instead of having to compile them every time the application is run.
28			If you are not using any private character tables (see the
29			<a href="pcre_maketables.html"><b>pcre_maketables()</b></a>
30			documentation), this is relatively straightforward. If you are using private
31	ph10	691	tables, it is a little bit more complicated. However, if you are using the
32	ph10	869	just-in-time optimization feature, it is not possible to save and reload the
33			JIT data.
34	nigel	75	</P>
35			<P>
36			If you save compiled patterns to a file, you can copy them to a different host
37	ph10	869	and run them there. If the two hosts have different endianness (byte order),
38	ph10	1194	you should run the <b>pcre[16\|32]_pattern_to_host_byte_order()</b> function on the
39	ph10	869	new host before trying to match the pattern. The matching functions return
40			PCRE_ERROR_BADENDIANNESS if they detect a pattern with the wrong endianness.
41	nigel	75	</P>
42	ph10	869	<P>
43			Compiling regular expressions with one version of PCRE for use with a different
44			version is not guaranteed to work and may cause crashes, and saving and
45			restoring a compiled pattern loses any JIT optimization data.
46			</P>
47	nigel	75	<br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
48			<P>
49	ph10	1194	The value returned by <b>pcre[16\|32]_compile()</b> points to a single block of
50	ph10	869	memory that holds the compiled pattern and associated data. You can find the
51	ph10	1194	length of this block in bytes by calling <b>pcre[16\|32]_fullinfo()</b> with an
52	ph10	869	argument of PCRE_INFO_SIZE. You can then save the data in any appropriate
53			manner. Here is sample code for the 8-bit library that compiles a pattern and
54			writes it to a file. It assumes that the variable <i>fd</i> refers to a file
55			that is open for output:
56	nigel	75	<pre>
57			int erroroffset, rc, size;
58			char *error;
59			pcre *re;
60
61			re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
62			if (re == NULL) { ... handle errors ... }
63			rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
64			if (rc < 0) { ... handle errors ... }
65			rc = fwrite(re, 1, size, fd);
66			if (rc != size) { ... handle errors ... }
67			</pre>
68			In this example, the bytes that comprise the compiled pattern are copied
69			exactly. Note that this is binary data that may contain any of the 256 possible
70			byte values. On systems that make a distinction between binary and non-binary
71			data, be sure that the file is opened for binary output.
72			</P>
73			<P>
74			If you want to write more than one pattern to a file, you will have to devise a
75			way of separating them. For binary data, preceding each pattern with its length
76			is probably the most straightforward approach. Another possibility is to write
77			out the data in hexadecimal instead of binary, one pattern to a line.
78			</P>
79			<P>
80			Saving compiled patterns in a file is only one possible way of storing them for
81			later use. They could equally well be saved in a database, or in the memory of
82			some daemon process that passes them via sockets to the processes that want
83			them.
84			</P>
85			<P>
86	ph10	691	If the pattern has been studied, it is also possible to save the normal study
87			data in a similar way to the compiled pattern itself. However, if the
88			PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is created cannot
89			be saved because it is too dependent on the current environment. When studying
90	ph10	1194	generates additional information, <b>pcre[16\|32]_study()</b> returns a pointer to a
91			<b>pcre[16\|32]_extra</b> data block. Its format is defined in the
92	nigel	75	<a href="pcreapi.html#extradata">section on matching a pattern</a>
93			in the
94			<a href="pcreapi.html"><b>pcreapi</b></a>
95			documentation. The <i>study_data</i> field points to the binary study data, and
96	ph10	1194	this is what you must save (not the <b>pcre[16\|32]_extra</b> block itself). The
97			length of the study data can be obtained by calling <b>pcre[16\|32]_fullinfo()</b>
98	ph10	869	with an argument of PCRE_INFO_STUDYSIZE. Remember to check that
99	ph10	1194	<b>pcre[16\|32]_study()</b> did return a non-NULL value before trying to save the
100	ph10	869	study data.
101	nigel	75	</P>
102			<br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
103			<P>
104			Re-using a precompiled pattern is straightforward. Having reloaded it into main
105	ph10	1194	memory, called <b>pcre[16\|32]_pattern_to_host_byte_order()</b> if necessary,
106			you pass its pointer to <b>pcre[16\|32]_exec()</b> or <b>pcre[16\|32]_dfa_exec()</b> in
107	ph10	869	the usual way.
108	nigel	75	</P>
109			<P>
110			However, if you passed a pointer to custom character tables when the pattern
111	ph10	1194	was compiled (the <i>tableptr</i> argument of <b>pcre[16\|32]_compile()</b>), you
112			must now pass a similar pointer to <b>pcre[16\|32]_exec()</b> or
113			<b>pcre[16\|32]_dfa_exec()</b>, because the value saved with the compiled pattern
114			will obviously be nonsense. A field in a <b>pcre[16\|32]_extra()</b> block is used
115	ph10	869	to pass this data, as described in the
116	nigel	75	<a href="pcreapi.html#extradata">section on matching a pattern</a>
117			in the
118			<a href="pcreapi.html"><b>pcreapi</b></a>
119			documentation.
120			</P>
121			<P>
122			If you did not provide custom character tables when the pattern was compiled,
123	ph10	903	the pointer in the compiled pattern is NULL, which causes the matching
124	ph10	869	functions to use PCRE's internal tables. Thus, you do not need to take any
125			special action at run time in this case.
126	nigel	75	</P>
127			<P>
128			If you saved study data with the compiled pattern, you need to create your own
129	ph10	1194	<b>pcre[16\|32]_extra</b> data block and set the <i>study_data</i> field to point to the
130	nigel	75	reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
131			<i>flags</i> field to indicate that study data is present. Then pass the
132	ph10	1194	<b>pcre[16\|32]_extra</b> block to the matching function in the usual way. If the
133	ph10	869	pattern was studied for just-in-time optimization, that data cannot be saved,
134			and so is lost by a save/restore cycle.
135	nigel	75	</P>
136			<br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
137			<P>
138	ph10	182	In general, it is safest to recompile all saved patterns when you update to a
139	ph10	579	new PCRE release, though not all updates actually require this.
140	nigel	75	</P>
141	ph10	99	<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
142	nigel	93	<P>
143	ph10	99	Philip Hazel
144	nigel	75	<br>
145	ph10	99	University Computing Service
146			<br>
147			Cambridge CB2 3QH, England.
148			<br>
149			</P>
150			<br><a name="SEC6" href="#TOC1">REVISION</a><br>
151			<P>
152	ph10	1194	Last updated: 24 June 2012
153	ph10	99	<br>
154	ph10	869	Copyright © 1997-2012 University of Cambridge.
155	ph10	99	<br>
156	nigel	75	<p>
157			Return to the <a href="index.html">PCRE index page</a>.
158			</p>
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