/[pcre]/code/trunk/doc/html/pcreprecompile.html
ViewVC logotype

Contents of /code/trunk/doc/html/pcreprecompile.html

Parent Directory Parent Directory | Revision Log Revision Log


Revision 1404 - (hide annotations) (download) (as text)
Tue Nov 19 15:36:57 2013 UTC (12 months, 4 weeks ago) by ph10
File MIME type: text/html
File size: 7399 byte(s)
Source tidies for 8.34-RC1.

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 &#60; 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 1404 memory, called <b>pcre[16|32]_pattern_to_host_byte_order()</b> if necessary, you
106     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 ph10 1404 <b>Warning:</b> The tables that <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b> use
123     must be the same as those that were used when the pattern was compiled. If this
124     is not the case, the behaviour is undefined.
125     </P>
126     <P>
127 nigel 75 If you did not provide custom character tables when the pattern was compiled,
128 ph10 903 the pointer in the compiled pattern is NULL, which causes the matching
129 ph10 869 functions to use PCRE's internal tables. Thus, you do not need to take any
130     special action at run time in this case.
131 nigel 75 </P>
132     <P>
133     If you saved study data with the compiled pattern, you need to create your own
134 ph10 1404 <b>pcre[16|32]_extra</b> data block and set the <i>study_data</i> field to point
135     to the reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in
136     the <i>flags</i> field to indicate that study data is present. Then pass the
137 ph10 1194 <b>pcre[16|32]_extra</b> block to the matching function in the usual way. If the
138 ph10 869 pattern was studied for just-in-time optimization, that data cannot be saved,
139     and so is lost by a save/restore cycle.
140 nigel 75 </P>
141     <br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
142     <P>
143 ph10 182 In general, it is safest to recompile all saved patterns when you update to a
144 ph10 579 new PCRE release, though not all updates actually require this.
145 nigel 75 </P>
146 ph10 99 <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
147 nigel 93 <P>
148 ph10 99 Philip Hazel
149 nigel 75 <br>
150 ph10 99 University Computing Service
151     <br>
152     Cambridge CB2 3QH, England.
153     <br>
154     </P>
155     <br><a name="SEC6" href="#TOC1">REVISION</a><br>
156     <P>
157 ph10 1404 Last updated: 12 November 2013
158 ph10 99 <br>
159 ph10 1404 Copyright &copy; 1997-2013 University of Cambridge.
160 ph10 99 <br>
161 nigel 75 <p>
162     Return to the <a href="index.html">PCRE index page</a>.
163     </p>

Properties

Name Value
svn:eol-style native
svn:keywords "Author Date Id Revision Url"

webmaster@exim.org
ViewVC Help
Powered by ViewVC 1.1.12