/[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 75 - (show annotations) (download) (as text)
Sat Feb 24 21:40:37 2007 UTC (7 years, 9 months ago) by nigel
File MIME type: text/html
File size: 6277 byte(s)
Load pcre-5.0 into code/trunk.

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 &#60; 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> in the usual way. This should
92 work even on another host, and even if that host has the opposite endianness to
93 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>, because the value saved with
99 the compiled pattern will obviously be nonsense. A field in a
100 <b>pcre_extra()</b> block is used to pass this data, as described in the
101 <a href="pcreapi.html#extradata">section on matching a pattern</a>
102 in the
103 <a href="pcreapi.html"><b>pcreapi</b></a>
104 documentation.
105 </P>
106 <P>
107 If you did not provide custom character tables when the pattern was compiled,
108 the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to
109 use PCRE's internal tables. Thus, you do not need to take any special action at
110 run time in this case.
111 </P>
112 <P>
113 If you saved study data with the compiled pattern, you need to create your own
114 <b>pcre_extra</b> data block and set the <i>study_data</i> field to point to the
115 reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
116 <i>flags</i> field to indicate that study data is present. Then pass the
117 <b>pcre_extra</b> block to <b>pcre_exec()</b> in the usual way.
118 </P>
119 <br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
120 <P>
121 The layout of the control block that is at the start of the data that makes up
122 a compiled pattern was changed for release 5.0. If you have any saved patterns
123 that were compiled with previous releases (not a facility that was previously
124 advertised), you will have to recompile them for release 5.0. However, from now
125 on, it should be possible to make changes in a compabible manner.
126 </P>
127 <P>
128 Last updated: 10 September 2004
129 <br>
130 Copyright &copy; 1997-2004 University of Cambridge.
131 <p>
132 Return to the <a href="index.html">PCRE index page</a>.
133 </p>

webmaster@exim.org
ViewVC Help
Powered by ViewVC 1.1.12