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>
</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.
</P>
<P>
If you save compiled patterns to a file, you can copy them to a different host
and run them there. This works even if the new host has the opposite endianness
to the one on which the patterns were compiled. There may be a small
performance penalty, but it should be insignificant.
</P>
<br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
<P>
The value returned by <b>pcre_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_fullinfo()</b> with an argument of
PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is
sample code 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 study data in
a similar way to the compiled pattern itself. When studying generates
additional information, <b>pcre_study()</b> returns a pointer to a
<b>pcre_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_extra</b> block itself). The length
of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an
argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_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, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in
the usual way. This should work even on another host, and even if that host has
the opposite endianness to the one where the pattern was compiled.
</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_compile()</b>), you must
now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>,
because the value saved with the compiled pattern will obviously be nonsense. A
field in a <b>pcre_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 <b>pcre_exec()</b> 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_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_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the
usual way.
</P>
<br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
<P>
The layout of the control block that is at the start of the data that makes up
a compiled pattern was changed for release 5.0. If you have any saved patterns
that were compiled with previous releases (not a facility that was previously
advertised), you will have to recompile them for release 5.0. However, from now
on, it should be possible to make changes in a compatible manner.
</P>
<P>
Last updated: 28 February 2005
<br>
Copyright &copy; 1997-2005 University of Cambridge.
<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			<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">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			</ul>
21			<br><a name="SEC1" href="#TOC1">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a><br>
22			<P>
23			If you are running an application that uses a large number of regular
24			expression patterns, it may be useful to store them in a precompiled form
25			instead of having to compile them every time the application is run.
26			If you are not using any private character tables (see the
27			<a href="pcre_maketables.html"><b>pcre_maketables()</b></a>
28			documentation), this is relatively straightforward. If you are using private
29			tables, it is a little bit more complicated.
30			</P>
31			<P>
32			If you save compiled patterns to a file, you can copy them to a different host
33			and run them there. This works even if the new host has the opposite endianness
34			to the one on which the patterns were compiled. There may be a small
35			performance penalty, but it should be insignificant.
36			</P>
37			<br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
38			<P>
39			The value returned by <b>pcre_compile()</b> points to a single block of memory
40			that holds the compiled pattern and associated data. You can find the length of
41			this block in bytes by calling <b>pcre_fullinfo()</b> with an argument of
42			PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is
43			sample code that compiles a pattern and writes it to a file. It assumes that
44			the variable <i>fd</i> refers to a file that is open for output:
45			<pre>
46			int erroroffset, rc, size;
47			char *error;
48			pcre *re;
49
50			re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
51			if (re == NULL) { ... handle errors ... }
52			rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
53			if (rc < 0) { ... handle errors ... }
54			rc = fwrite(re, 1, size, fd);
55			if (rc != size) { ... handle errors ... }
56			</pre>
57			In this example, the bytes that comprise the compiled pattern are copied
58			exactly. Note that this is binary data that may contain any of the 256 possible
59			byte values. On systems that make a distinction between binary and non-binary
60			data, be sure that the file is opened for binary output.
61			</P>
62			<P>
63			If you want to write more than one pattern to a file, you will have to devise a
64			way of separating them. For binary data, preceding each pattern with its length
65			is probably the most straightforward approach. Another possibility is to write
66			out the data in hexadecimal instead of binary, one pattern to a line.
67			</P>
68			<P>
69			Saving compiled patterns in a file is only one possible way of storing them for
70			later use. They could equally well be saved in a database, or in the memory of
71			some daemon process that passes them via sockets to the processes that want
72			them.
73			</P>
74			<P>
75			If the pattern has been studied, it is also possible to save the study data in
76			a similar way to the compiled pattern itself. When studying generates
77			additional information, <b>pcre_study()</b> returns a pointer to a
78			<b>pcre_extra</b> data block. Its format is defined in the
79			<a href="pcreapi.html#extradata">section on matching a pattern</a>
80			in the
81			<a href="pcreapi.html"><b>pcreapi</b></a>
82			documentation. The <i>study_data</i> field points to the binary study data, and
83			this is what you must save (not the <b>pcre_extra</b> block itself). The length
84			of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an
85			argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_study()</b> did
86			return a non-NULL value before trying to save the study data.
87			</P>
88			<br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
89			<P>
90			Re-using a precompiled pattern is straightforward. Having reloaded it into main
91	nigel	77	memory, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in
92			the usual way. This should work even on another host, and even if that host has
93			the opposite endianness to the one where the pattern was compiled.
94	nigel	75	</P>
95			<P>
96			However, if you passed a pointer to custom character tables when the pattern
97			was compiled (the <i>tableptr</i> argument of <b>pcre_compile()</b>), you must
98	nigel	77	now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>,
99			because the value saved with the compiled pattern will obviously be nonsense. A
100			field in a <b>pcre_extra()</b> block is used to pass this data, as described in
101			the
102	nigel	75	<a href="pcreapi.html#extradata">section on matching a pattern</a>
103			in the
104			<a href="pcreapi.html"><b>pcreapi</b></a>
105			documentation.
106			</P>
107			<P>
108			If you did not provide custom character tables when the pattern was compiled,
109			the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to
110			use PCRE's internal tables. Thus, you do not need to take any special action at
111			run time in this case.
112			</P>
113			<P>
114			If you saved study data with the compiled pattern, you need to create your own
115			<b>pcre_extra</b> data block and set the <i>study_data</i> field to point to the
116			reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
117			<i>flags</i> field to indicate that study data is present. Then pass the
118	nigel	77	<b>pcre_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the
119			usual way.
120	nigel	75	</P>
121			<br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
122			<P>
123			The layout of the control block that is at the start of the data that makes up
124			a compiled pattern was changed for release 5.0. If you have any saved patterns
125			that were compiled with previous releases (not a facility that was previously
126			advertised), you will have to recompile them for release 5.0. However, from now
127	nigel	79	on, it should be possible to make changes in a compatible manner.
128	nigel	75	</P>
129			<P>
130	nigel	77	Last updated: 28 February 2005
131	nigel	75	<br>
132	nigel	77	Copyright © 1997-2005 University of Cambridge.
133	nigel	75	<p>
134			Return to the <a href="index.html">PCRE index page</a>.
135			</p>