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 and above.
</P>
<P>
If you have any saved patterns in UTF-8 mode that use \p or \P that were
compiled with any release up to and including 6.4, you will have to recompile
them for release 6.5 and above.
</P>
<P>
All saved patterns from earlier releases must be recompiled for release 7.0 or
higher, because there was an internal reorganization at that release.
</P>
<P>
Last updated: 28 November 2006
<br>
Copyright &copy; 1997-2006 University of Cambridge.
<p>
Return to the <a href="index.html">PCRE index page</a>.
</p>
1	<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	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	</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	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	<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	<b>pcre_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the
119	usual way.
120	</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 and above.
127	</P>
128	<P>
129	If you have any saved patterns in UTF-8 mode that use \p or \P that were
130	compiled with any release up to and including 6.4, you will have to recompile
131	them for release 6.5 and above.
132	</P>
133	<P>
134	All saved patterns from earlier releases must be recompiled for release 7.0 or
135	higher, because there was an internal reorganization at that release.
136	</P>
137	<P>
138	Last updated: 28 November 2006
139	<br>
140	Copyright © 1997-2006 University of Cambridge.
141	<p>
142	Return to the <a href="index.html">PCRE index page</a>.
143	</p>
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