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. 129 </P> 130 <br><a name="SEC5" href="#TOC1">AUTHOR</a><br> 131 <P> 132 Philip Hazel 133 <br> 134 University Computing Service 135 <br> 136 Cambridge CB2 3QH, England. 137 <br> 138 </P> 139 <br><a name="SEC6" href="#TOC1">REVISION</a><br> 140 <P> 141 Last updated: 17 November 2010 142 <br> 143 Copyright © 1997-2010 University of Cambridge. 144 <br> 145 <p> 146 Return to the <a href="index.html">PCRE index page</a>. 147 </p> 148
