|
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. However, compiling regular |
|
38 expressions with one version of PCRE for use with a different version is not |
|
39 guaranteed to work and may cause crashes. |
|
40 </P> |
|
41 <br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br> |
|
42 <P> |
|
43 The value returned by <b>pcre_compile()</b> points to a single block of memory |
|
44 that holds the compiled pattern and associated data. You can find the length of |
|
45 this block in bytes by calling <b>pcre_fullinfo()</b> with an argument of |
|
46 PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is |
|
47 sample code that compiles a pattern and writes it to a file. It assumes that |
|
48 the variable <i>fd</i> refers to a file that is open for output: |
|
49 <pre> |
|
50 int erroroffset, rc, size; |
|
51 char *error; |
|
52 pcre *re; |
|
53 |
|
54 re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL); |
|
55 if (re == NULL) { ... handle errors ... } |
|
56 rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size); |
|
57 if (rc < 0) { ... handle errors ... } |
|
58 rc = fwrite(re, 1, size, fd); |
|
59 if (rc != size) { ... handle errors ... } |
|
60 </pre> |
|
61 In this example, the bytes that comprise the compiled pattern are copied |
|
62 exactly. Note that this is binary data that may contain any of the 256 possible |
|
63 byte values. On systems that make a distinction between binary and non-binary |
|
64 data, be sure that the file is opened for binary output. |
|
65 </P> |
|
66 <P> |
|
67 If you want to write more than one pattern to a file, you will have to devise a |
|
68 way of separating them. For binary data, preceding each pattern with its length |
|
69 is probably the most straightforward approach. Another possibility is to write |
|
70 out the data in hexadecimal instead of binary, one pattern to a line. |
|
71 </P> |
|
72 <P> |
|
73 Saving compiled patterns in a file is only one possible way of storing them for |
|
74 later use. They could equally well be saved in a database, or in the memory of |
|
75 some daemon process that passes them via sockets to the processes that want |
|
76 them. |
|
77 </P> |
|
78 <P> |
|
79 If the pattern has been studied, it is also possible to save the study data in |
|
80 a similar way to the compiled pattern itself. When studying generates |
|
81 additional information, <b>pcre_study()</b> returns a pointer to a |
|
82 <b>pcre_extra</b> data block. Its format is defined in the |
|
83 <a href="pcreapi.html#extradata">section on matching a pattern</a> |
|
84 in the |
|
85 <a href="pcreapi.html"><b>pcreapi</b></a> |
|
86 documentation. The <i>study_data</i> field points to the binary study data, and |
|
87 this is what you must save (not the <b>pcre_extra</b> block itself). The length |
|
88 of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an |
|
89 argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_study()</b> did |
|
90 return a non-NULL value before trying to save the study data. |
|
91 </P> |
|
92 <br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br> |
|
93 <P> |
|
94 Re-using a precompiled pattern is straightforward. Having reloaded it into main |
|
95 memory, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in |
|
96 the usual way. This should work even on another host, and even if that host has |
|
97 the opposite endianness to the one where the pattern was compiled. |
|
98 </P> |
|
99 <P> |
|
100 However, if you passed a pointer to custom character tables when the pattern |
|
101 was compiled (the <i>tableptr</i> argument of <b>pcre_compile()</b>), you must |
|
102 now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>, |
|
103 because the value saved with the compiled pattern will obviously be nonsense. A |
|
104 field in a <b>pcre_extra()</b> block is used to pass this data, as described in |
|
105 the |
|
106 <a href="pcreapi.html#extradata">section on matching a pattern</a> |
|
107 in the |
|
108 <a href="pcreapi.html"><b>pcreapi</b></a> |
|
109 documentation. |
|
110 </P> |
|
111 <P> |
|
112 If you did not provide custom character tables when the pattern was compiled, |
|
113 the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to |
|
114 use PCRE's internal tables. Thus, you do not need to take any special action at |
|
115 run time in this case. |
|
116 </P> |
|
117 <P> |
|
118 If you saved study data with the compiled pattern, you need to create your own |
|
119 <b>pcre_extra</b> data block and set the <i>study_data</i> field to point to the |
|
120 reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the |
|
121 <i>flags</i> field to indicate that study data is present. Then pass the |
|
122 <b>pcre_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the |
|
123 usual way. |
|
124 </P> |
|
125 <br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br> |
|
126 <P> |
|
127 In general, it is safest to recompile all saved patterns when you update to a |
|
128 new PCRE release, though not all updates actually require this. Recompiling is |
|
129 definitely needed for release 7.2. |
|
130 </P> |
|
131 <br><a name="SEC5" href="#TOC1">AUTHOR</a><br> |
|
132 <P> |
|
133 Philip Hazel |
|
134 <br> |
|
135 University Computing Service |
|
136 <br> |
|
137 Cambridge CB2 3QH, England. |
|
138 <br> |
|
139 </P> |
|
140 <br><a name="SEC6" href="#TOC1">REVISION</a><br> |
|
141 <P> |
|
142 Last updated: 13 June 2007 |
|
143 <br> |
|
144 Copyright © 1997-2007 University of Cambridge. |
|
145 <br> |
|
146 <p> |
|
147 Return to the <a href="index.html">PCRE index page</a>. |
|
148 </p> |