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> 8Return to the <a href="index.html">PCRE index page</a>. 9</p> 10<p> 11This page is part of the PCRE HTML documentation. It was generated automatically 12from the original man page. If there is any nonsense in it, please consult the 13man 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> 25If you are running an application that uses a large number of regular 26expression patterns, it may be useful to store them in a precompiled form 27instead of having to compile them every time the application is run. 28If you are not using any private character tables (see the 29<a href="pcre_maketables.html"><b>pcre_maketables()</b></a> 30documentation), this is relatively straightforward. If you are using private 31tables, it is a little bit more complicated. 32</P> 33<P> 34If you save compiled patterns to a file, you can copy them to a different host 35and run them there. This works even if the new host has the opposite endianness 36to the one on which the patterns were compiled. There may be a small 37performance penalty, but it should be insignificant. However, compiling regular 38expressions with one version of PCRE for use with a different version is not 39guaranteed to work and may cause crashes. 40</P> 41<br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br> 42<P> 43The value returned by <b>pcre_compile()</b> points to a single block of memory 44that holds the compiled pattern and associated data. You can find the length of 45this block in bytes by calling <b>pcre_fullinfo()</b> with an argument of 46PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is 47sample code that compiles a pattern and writes it to a file. It assumes that 48the 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> 61In this example, the bytes that comprise the compiled pattern are copied 62exactly. Note that this is binary data that may contain any of the 256 possible 63byte values. On systems that make a distinction between binary and non-binary 64data, be sure that the file is opened for binary output. 65</P> 66<P> 67If you want to write more than one pattern to a file, you will have to devise a 68way of separating them. For binary data, preceding each pattern with its length 69is probably the most straightforward approach. Another possibility is to write 70out the data in hexadecimal instead of binary, one pattern to a line. 71</P> 72<P> 73Saving compiled patterns in a file is only one possible way of storing them for 74later use. They could equally well be saved in a database, or in the memory of 75some daemon process that passes them via sockets to the processes that want 76them. 77</P> 78<P> 79If the pattern has been studied, it is also possible to save the study data in 80a similar way to the compiled pattern itself. When studying generates 81additional 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> 84in the 85<a href="pcreapi.html"><b>pcreapi</b></a> 86documentation. The <i>study_data</i> field points to the binary study data, and 87this is what you must save (not the <b>pcre_extra</b> block itself). The length 88of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an 89argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_study()</b> did 90return 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> 94Re-using a precompiled pattern is straightforward. Having reloaded it into main 95memory, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in 96the usual way. This should work even on another host, and even if that host has 97the opposite endianness to the one where the pattern was compiled. 98</P> 99<P> 100However, if you passed a pointer to custom character tables when the pattern 101was compiled (the <i>tableptr</i> argument of <b>pcre_compile()</b>), you must 102now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>, 103because the value saved with the compiled pattern will obviously be nonsense. A 104field in a <b>pcre_extra()</b> block is used to pass this data, as described in 105the 106<a href="pcreapi.html#extradata">section on matching a pattern</a> 107in the 108<a href="pcreapi.html"><b>pcreapi</b></a> 109documentation. 110</P> 111<P> 112If you did not provide custom character tables when the pattern was compiled, 113the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to 114use PCRE's internal tables. Thus, you do not need to take any special action at 115run time in this case. 116</P> 117<P> 118If 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 120reloaded 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 123usual way. 124</P> 125<br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br> 126<P> 127In general, it is safest to recompile all saved patterns when you update to a 128new PCRE release, though not all updates actually require this. Recompiling is 129definitely needed for release 7.2. 130</P> 131<br><a name="SEC5" href="#TOC1">AUTHOR</a><br> 132<P> 133Philip Hazel 134<br> 135University Computing Service 136<br> 137Cambridge CB2 3QH, England. 138<br> 139</P> 140<br><a name="SEC6" href="#TOC1">REVISION</a><br> 141<P> 142Last updated: 13 June 2007 143<br> 144Copyright © 1997-2007 University of Cambridge. 145<br> 146<p> 147Return to the <a href="index.html">PCRE index page</a>. 148</p> 149