/[pcre]/code/tags/pcre-4.5/doc/pcrebuild.3
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Tag code/trunk as code/tags/pcre-4.5.

1 nigel 63 .TH PCRE 3
2     .SH NAME
3     PCRE - Perl-compatible regular expressions
4     .SH PCRE BUILD-TIME OPTIONS
5     .rs
6     .sp
7     This document describes the optional features of PCRE that can be selected when
8     the library is compiled. They are all selected, or deselected, by providing
9     options to the \fBconfigure\fR script which is run before the \fBmake\fR
10     command. The complete list of options for \fBconfigure\fR (which includes the
11     standard ones such as the selection of the installation directory) can be
12     obtained by running
13    
14     ./configure --help
15    
16     The following sections describe certain options whose names begin with --enable
17     or --disable. These settings specify changes to the defaults for the
18     \fBconfigure\fR command. Because of the way that \fBconfigure\fR works,
19     --enable and --disable always come in pairs, so the complementary option always
20     exists as well, but as it specifies the default, it is not described.
21    
22     .SH UTF-8 SUPPORT
23     .rs
24     .sp
25     To build PCRE with support for UTF-8 character strings, add
26    
27     --enable-utf8
28    
29     to the \fBconfigure\fR command. Of itself, this does not make PCRE treat
30     strings as UTF-8. As well as compiling PCRE with this option, you also have
31     have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fR
32     function.
33    
34     .SH CODE VALUE OF NEWLINE
35     .rs
36     .sp
37     By default, PCRE treats character 10 (linefeed) as the newline character. This
38     is the normal newline character on Unix-like systems. You can compile PCRE to
39     use character 13 (carriage return) instead by adding
40    
41     --enable-newline-is-cr
42    
43     to the \fBconfigure\fR command. For completeness there is also a
44     --enable-newline-is-lf option, which explicitly specifies linefeed as the
45     newline character.
46    
47     .SH BUILDING SHARED AND STATIC LIBRARIES
48     .rs
49     .sp
50     The PCRE building process uses \fBlibtool\fR to build both shared and static
51     Unix libraries by default. You can suppress one of these by adding one of
52    
53     --disable-shared
54     --disable-static
55    
56     to the \fBconfigure\fR command, as required.
57    
58     .SH POSIX MALLOC USAGE
59     .rs
60     .sp
61     When PCRE is called through the POSIX interface (see the \fBpcreposix\fR
62     documentation), additional working storage is required for holding the pointers
63     to capturing substrings because PCRE requires three integers per substring,
64     whereas the POSIX interface provides only two. If the number of expected
65     substrings is small, the wrapper function uses space on the stack, because this
66     is faster than using \fBmalloc()\fR for each call. The default threshold above
67     which the stack is no longer used is 10; it can be changed by adding a setting
68     such as
69    
70     --with-posix-malloc-threshold=20
71    
72     to the \fBconfigure\fR command.
73    
74     .SH LIMITING PCRE RESOURCE USAGE
75     .rs
76     .sp
77     Internally, PCRE has a function called \fBmatch()\fR which it calls repeatedly
78     (possibly recursively) when performing a matching operation. By limiting the
79     number of times this function may be called, a limit can be placed on the
80     resources used by a single call to \fBpcre_exec()\fR. The limit can be changed
81     at run time, as described in the \fBpcreapi\fR documentation. The default is 10
82     million, but this can be changed by adding a setting such as
83    
84     --with-match-limit=500000
85    
86     to the \fBconfigure\fR command.
87    
88     .SH HANDLING VERY LARGE PATTERNS
89     .rs
90     .sp
91     Within a compiled pattern, offset values are used to point from one part to
92     another (for example, from an opening parenthesis to an alternation
93     metacharacter). By default two-byte values are used for these offsets, leading
94     to a maximum size for a compiled pattern of around 64K. This is sufficient to
95     handle all but the most gigantic patterns. Nevertheless, some people do want to
96     process enormous patterns, so it is possible to compile PCRE to use three-byte
97     or four-byte offsets by adding a setting such as
98    
99     --with-link-size=3
100    
101     to the \fBconfigure\fR command. The value given must be 2, 3, or 4. Using
102     longer offsets slows down the operation of PCRE because it has to load
103     additional bytes when handling them.
104    
105     If you build PCRE with an increased link size, test 2 (and test 5 if you are
106     using UTF-8) will fail. Part of the output of these tests is a representation
107     of the compiled pattern, and this changes with the link size.
108    
109 nigel 73 .SH AVOIDING EXCESSIVE STACK USAGE
110     .rs
111     .sp
112     PCRE implements backtracking while matching by making recursive calls to an
113     internal function called \fBmatch()\fR. In environments where the size of the
114     stack is limited, this can severely limit PCRE's operation. (The Unix
115     environment does not usually suffer from this problem.) An alternative approach
116     that uses memory from the heap to remember data, instead of using recursive
117     function calls, has been implemented to work round this problem. If you want to
118     build a version of PCRE that works this way, add
119    
120     --disable-stack-for-recursion
121    
122     to the \fBconfigure\fR command. With this configuration, PCRE will use the
123     \fBpcre_stack_malloc\fR and \fBpcre_stack_free\fR variables to call memory
124     management functions. Separate functions are provided because the usage is very
125     predictable: the block sizes requested are always the same, and the blocks are
126     always freed in reverse order. A calling program might be able to implement
127     optimized functions that perform better than the standard \fBmalloc()\fR and
128     \fBfree()\fR functions. PCRE runs noticeably more slowly when built in this
129     way.
130    
131     .SH USING EBCDIC CODE
132     .rs
133     .sp
134     PCRE assumes by default that it will run in an environment where the character
135     code is ASCII (or UTF-8, which is a superset of ASCII). PCRE can, however, be
136     compiled to run in an EBCDIC environment by adding
137    
138     --enable-ebcdic
139    
140     to the \fBconfigure\fR command.
141    
142 nigel 63 .in 0
143 nigel 73 Last updated: 09 December 2003
144 nigel 63 .br
145     Copyright (c) 1997-2003 University of Cambridge.

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