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Tag code/trunk as code/tags/pcre-6.3.
3 PCRE - Perl-compatible regular expressions
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\fP script that is run before the \fBmake\fP
10 command. The complete list of options for \fBconfigure\fP (which includes the
11 standard ones such as the selection of the installation directory) can be
12 obtained by running
13 .sp
14 ./configure --help
15 .sp
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\fP command. Because of the way that \fBconfigure\fP 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 "C++ SUPPORT"
23 .rs
24 .sp
25 By default, the \fBconfigure\fP script will search for a C++ compiler and C++
26 header files. If it finds them, it automatically builds the C++ wrapper library
27 for PCRE. You can disable this by adding
28 .sp
29 --disable-cpp
30 .sp
31 to the \fBconfigure\fP command.
32 .
34 .rs
35 .sp
36 To build PCRE with support for UTF-8 character strings, add
37 .sp
38 --enable-utf8
39 .sp
40 to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
41 strings as UTF-8. As well as compiling PCRE with this option, you also have
42 have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
43 function.
44 .
46 .rs
47 .sp
48 UTF-8 support allows PCRE to process character values greater than 255 in the
49 strings that it handles. On its own, however, it does not provide any
50 facilities for accessing the properties of such characters. If you want to be
51 able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
52 character properties, you must add
53 .sp
54 --enable-unicode-properties
55 .sp
56 to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
57 not explicitly requested it.
58 .P
59 Including Unicode property support adds around 90K of tables to the PCRE
60 library, approximately doubling its size. Only the general category properties
61 such as \fILu\fP and \fINd\fP are supported. Details are given in the
62 .\" HREF
63 \fBpcrepattern\fP
64 .\"
65 documentation.
66 .
68 .rs
69 .sp
70 By default, PCRE treats character 10 (linefeed) as the newline character. This
71 is the normal newline character on Unix-like systems. You can compile PCRE to
72 use character 13 (carriage return) instead by adding
73 .sp
74 --enable-newline-is-cr
75 .sp
76 to the \fBconfigure\fP command. For completeness there is also a
77 --enable-newline-is-lf option, which explicitly specifies linefeed as the
78 newline character.
79 .
81 .rs
82 .sp
83 The PCRE building process uses \fBlibtool\fP to build both shared and static
84 Unix libraries by default. You can suppress one of these by adding one of
85 .sp
86 --disable-shared
87 --disable-static
88 .sp
89 to the \fBconfigure\fP command, as required.
90 .
92 .rs
93 .sp
94 When PCRE is called through the POSIX interface (see the
95 .\" HREF
96 \fBpcreposix\fP
97 .\"
98 documentation), additional working storage is required for holding the pointers
99 to capturing substrings, because PCRE requires three integers per substring,
100 whereas the POSIX interface provides only two. If the number of expected
101 substrings is small, the wrapper function uses space on the stack, because this
102 is faster than using \fBmalloc()\fP for each call. The default threshold above
103 which the stack is no longer used is 10; it can be changed by adding a setting
104 such as
105 .sp
106 --with-posix-malloc-threshold=20
107 .sp
108 to the \fBconfigure\fP command.
109 .
111 .rs
112 .sp
113 Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
114 (possibly recursively) when matching a pattern with the \fBpcre_exec()\fP
115 function. By controlling the maximum number of times this function may be
116 called during a single matching operation, a limit can be placed on the
117 resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
118 at run time, as described in the
119 .\" HREF
120 \fBpcreapi\fP
121 .\"
122 documentation. The default is 10 million, but this can be changed by adding a
123 setting such as
124 .sp
125 --with-match-limit=500000
126 .sp
127 to the \fBconfigure\fP command. This setting has no effect on the
128 \fBpcre_dfa_exec()\fP matching function.
129 .
131 .rs
132 .sp
133 Within a compiled pattern, offset values are used to point from one part to
134 another (for example, from an opening parenthesis to an alternation
135 metacharacter). By default, two-byte values are used for these offsets, leading
136 to a maximum size for a compiled pattern of around 64K. This is sufficient to
137 handle all but the most gigantic patterns. Nevertheless, some people do want to
138 process enormous patterns, so it is possible to compile PCRE to use three-byte
139 or four-byte offsets by adding a setting such as
140 .sp
141 --with-link-size=3
142 .sp
143 to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
144 longer offsets slows down the operation of PCRE because it has to load
145 additional bytes when handling them.
146 .P
147 If you build PCRE with an increased link size, test 2 (and test 5 if you are
148 using UTF-8) will fail. Part of the output of these tests is a representation
149 of the compiled pattern, and this changes with the link size.
150 .
152 .rs
153 .sp
154 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
155 by making recursive calls to an internal function called \fBmatch()\fP. In
156 environments where the size of the stack is limited, this can severely limit
157 PCRE's operation. (The Unix environment does not usually suffer from this
158 problem.) An alternative approach that uses memory from the heap to remember
159 data, instead of using recursive function calls, has been implemented to work
160 round this problem. If you want to build a version of PCRE that works this way,
161 add
162 .sp
163 --disable-stack-for-recursion
164 .sp
165 to the \fBconfigure\fP command. With this configuration, PCRE will use the
166 \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
167 management functions. Separate functions are provided because the usage is very
168 predictable: the block sizes requested are always the same, and the blocks are
169 always freed in reverse order. A calling program might be able to implement
170 optimized functions that perform better than the standard \fBmalloc()\fP and
171 \fBfree()\fP functions. PCRE runs noticeably more slowly when built in this
172 way. This option affects only the \fBpcre_exec()\fP function; it is not
173 relevant for the the \fBpcre_dfa_exec()\fP function.
174 .
176 .rs
177 .sp
178 PCRE assumes by default that it will run in an environment where the character
179 code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
180 compiled to run in an EBCDIC environment by adding
181 .sp
182 --enable-ebcdic
183 .sp
184 to the \fBconfigure\fP command.
185 .P
186 .in 0
187 Last updated: 15 August 2005
188 .br
189 Copyright (c) 1997-2005 University of Cambridge.

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