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.
</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>
<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: 06 March 2007
<br>
Copyright &copy; 1997-2007 University of Cambridge.
<br>
<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	<li><a name="TOC5" href="#SEC5">AUTHOR</a>
21	<li><a name="TOC6" href="#SEC6">REVISION</a>
22	</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	tables, it is a little bit more complicated.
32	</P>
33	<P>
34	If you save compiled patterns to a file, you can copy them to a different host
35	and run them there. This works even if the new host has the opposite endianness
36	to the one on which the patterns were compiled. There may be a small
37	performance penalty, but it should be insignificant.
38	</P>
39	<br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
40	<P>
41	The value returned by <b>pcre_compile()</b> points to a single block of memory
42	that holds the compiled pattern and associated data. You can find the length of
43	this block in bytes by calling <b>pcre_fullinfo()</b> with an argument of
44	PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is
45	sample code that compiles a pattern and writes it to a file. It assumes that
46	the variable <i>fd</i> refers to a file that is open for output:
47	<pre>
48	int erroroffset, rc, size;
49	char *error;
50	pcre *re;
51
52	re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
53	if (re == NULL) { ... handle errors ... }
54	rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
55	if (rc < 0) { ... handle errors ... }
56	rc = fwrite(re, 1, size, fd);
57	if (rc != size) { ... handle errors ... }
58	</pre>
59	In this example, the bytes that comprise the compiled pattern are copied
60	exactly. Note that this is binary data that may contain any of the 256 possible
61	byte values. On systems that make a distinction between binary and non-binary
62	data, be sure that the file is opened for binary output.
63	</P>
64	<P>
65	If you want to write more than one pattern to a file, you will have to devise a
66	way of separating them. For binary data, preceding each pattern with its length
67	is probably the most straightforward approach. Another possibility is to write
68	out the data in hexadecimal instead of binary, one pattern to a line.
69	</P>
70	<P>
71	Saving compiled patterns in a file is only one possible way of storing them for
72	later use. They could equally well be saved in a database, or in the memory of
73	some daemon process that passes them via sockets to the processes that want
74	them.
75	</P>
76	<P>
77	If the pattern has been studied, it is also possible to save the study data in
78	a similar way to the compiled pattern itself. When studying generates
79	additional information, <b>pcre_study()</b> returns a pointer to a
80	<b>pcre_extra</b> data block. Its format is defined in the
81	<a href="pcreapi.html#extradata">section on matching a pattern</a>
82	in the
83	<a href="pcreapi.html"><b>pcreapi</b></a>
84	documentation. The <i>study_data</i> field points to the binary study data, and
85	this is what you must save (not the <b>pcre_extra</b> block itself). The length
86	of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an
87	argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_study()</b> did
88	return a non-NULL value before trying to save the study data.
89	</P>
90	<br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
91	<P>
92	Re-using a precompiled pattern is straightforward. Having reloaded it into main
93	memory, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in
94	the usual way. This should work even on another host, and even if that host has
95	the opposite endianness to the one where the pattern was compiled.
96	</P>
97	<P>
98	However, if you passed a pointer to custom character tables when the pattern
99	was compiled (the <i>tableptr</i> argument of <b>pcre_compile()</b>), you must
100	now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>,
101	because the value saved with the compiled pattern will obviously be nonsense. A
102	field in a <b>pcre_extra()</b> block is used to pass this data, as described in
103	the
104	<a href="pcreapi.html#extradata">section on matching a pattern</a>
105	in the
106	<a href="pcreapi.html"><b>pcreapi</b></a>
107	documentation.
108	</P>
109	<P>
110	If you did not provide custom character tables when the pattern was compiled,
111	the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to
112	use PCRE's internal tables. Thus, you do not need to take any special action at
113	run time in this case.
114	</P>
115	<P>
116	If you saved study data with the compiled pattern, you need to create your own
117	<b>pcre_extra</b> data block and set the <i>study_data</i> field to point to the
118	reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
119	<i>flags</i> field to indicate that study data is present. Then pass the
120	<b>pcre_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the
121	usual way.
122	</P>
123	<br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
124	<P>
125	The layout of the control block that is at the start of the data that makes up
126	a compiled pattern was changed for release 5.0. If you have any saved patterns
127	that were compiled with previous releases (not a facility that was previously
128	advertised), you will have to recompile them for release 5.0 and above.
129	</P>
130	<P>
131	If you have any saved patterns in UTF-8 mode that use \p or \P that were
132	compiled with any release up to and including 6.4, you will have to recompile
133	them for release 6.5 and above.
134	</P>
135	<P>
136	All saved patterns from earlier releases must be recompiled for release 7.0 or
137	higher, because there was an internal reorganization at that release.
138	</P>
139	<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
140	<P>
141	Philip Hazel
142	<br>
143	University Computing Service
144	<br>
145	Cambridge CB2 3QH, England.
146	<br>
147	</P>
148	<br><a name="SEC6" href="#TOC1">REVISION</a><br>
149	<P>
150	Last updated: 06 March 2007
151	<br>
152	Copyright © 1997-2007 University of Cambridge.
153	<br>
154	<p>
155	Return to the <a href="index.html">PCRE index page</a>.
156	</p>
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