1ExtUtils::Constant(3pm)Perl Programmers Reference GuideExtUtils::Constant(3pm)
2
6 ExtUtils::Constant - generate XS code to import C header constants
7
9 use ExtUtils::Constant qw (WriteConstants);
10 WriteConstants(
11 NAME => 'Foo',
12 NAMES => [qw(FOO BAR BAZ)],
13 );
14 # Generates wrapper code to make the values of the constants FOO BAR BAZ
15 # available to perl
16
18 ExtUtils::Constant facilitates generating C and XS wrapper code to
19 allow perl modules to AUTOLOAD constants defined in C library header
20 files. It is principally used by the "h2xs" utility, on which this
21 code is based. It doesn't contain the routines to scan header files to
22 extract these constants.
23
25 Generally one only needs to call the "WriteConstants" function, and
26 then
27 #include "const-c.inc"
29 in the C section of "Foo.xs"
31 INCLUDE: const-xs.inc
33 in the XS section of "Foo.xs".
35 For greater flexibility use "constant_types()", "C_constant" and
37 "XS_constant", with which "WriteConstants" is implemented.
38 Currently this module understands the following types. h2xs may only
40 know a subset. The sizes of the numeric types are chosen by the
41 "Configure" script at compile time.
42 IV signed integer, at least 32 bits.
44 UV unsigned integer, the same size as IV
46 NV floating point type, probably "double", possibly "long double"
48 PV NUL terminated string, length will be determined with "strlen"
50 PVN A fixed length thing, given as a [pointer, length] pair. If you
52 know the length of a string at compile time you may use this
53 instead of PV
54 SV A mortal SV.
56 YES Truth. ("PL_sv_yes") The value is not needed (and ignored).
58 NO Defined Falsehood. ("PL_sv_no") The value is not needed (and
60 ignored).
61 UNDEF
63 "undef". The value of the macro is not needed.
64
66 constant_types
67 A function returning a single scalar with "#define" definitions for
68 the constants used internally between the generated C and XS
69 functions.
70 XS_constant PACKAGE, TYPES, XS_SUBNAME, C_SUBNAME
72 A function to generate the XS code to implement the perl subroutine
73 PACKAGE::constant used by PACKAGE::AUTOLOAD to load constants.
74 This XS code is a wrapper around a C subroutine usually generated
75 by "C_constant", and usually named "constant".
76 TYPES should be given either as a comma separated list of types
78 that the C subroutine "constant" will generate or as a reference to
79 a hash. It should be the same list of types as "C_constant" was
80 given. [Otherwise "XS_constant" and "C_constant" may have
81 different ideas about the number of parameters passed to the C
82 function "constant"]
83 You can call the perl visible subroutine something other than
85 "constant" if you give the parameter XS_SUBNAME. The C subroutine
86 it calls defaults to the name of the perl visible subroutine,
87 unless you give the parameter C_SUBNAME.
88 autoload PACKAGE, VERSION, AUTOLOADER
90 A function to generate the AUTOLOAD subroutine for the module
91 PACKAGE VERSION is the perl version the code should be backwards
92 compatible with. It defaults to the version of perl running the
93 subroutine. If AUTOLOADER is true, the AUTOLOAD subroutine falls
94 back on AutoLoader::AUTOLOAD for all names that the constant()
95 routine doesn't recognise.
96 WriteMakefileSnippet
98 WriteMakefileSnippet ATTRIBUTE => VALUE [, ...]
99 A function to generate perl code for Makefile.PL that will
101 regenerate the constant subroutines. Parameters are named as
102 passed to "WriteConstants", with the addition of "INDENT" to
103 specify the number of leading spaces (default 2).
104 Currently only "INDENT", "NAME", "DEFAULT_TYPE", "NAMES", "C_FILE"
106 and "XS_FILE" are recognised.
107 WriteConstants ATTRIBUTE => VALUE [, ...]
109 Writes a file of C code and a file of XS code which you should
110 "#include" and "INCLUDE" in the C and XS sections respectively of
111 your module's XS code. You probably want to do this in your
112 "Makefile.PL", so that you can easily edit the list of constants
113 without touching the rest of your module. The attributes supported
114 are
115 NAME
117 Name of the module. This must be specified
118 DEFAULT_TYPE
120 The default type for the constants. If not specified "IV" is
121 assumed.
122 BREAKOUT_AT
124 The names of the constants are grouped by length. Generate
125 child subroutines for each group with this number or more names
126 in.
127 NAMES
129 An array of constants' names, either scalars containing names,
130 or hashrefs as detailed in "C_constant".
131 PROXYSUBS
133 If true, uses proxy subs. See ExtUtils::Constant::ProxySubs.
134 C_FH
136 A filehandle to write the C code to. If not given, then C_FILE
137 is opened for writing.
138 C_FILE
140 The name of the file to write containing the C code. The
141 default is "const-c.inc". The "-" in the name ensures that the
142 file can't be mistaken for anything related to a legitimate
143 perl package name, and not naming the file ".c" avoids having
144 to override Makefile.PL's ".xs" to ".c" rules.
145 XS_FH
147 A filehandle to write the XS code to. If not given, then
148 XS_FILE is opened for writing.
149 XS_FILE
151 The name of the file to write containing the XS code. The
152 default is "const-xs.inc".
153 XS_SUBNAME
155 The perl visible name of the XS subroutine generated which will
156 return the constants. The default is "constant".
157 C_SUBNAME
159 The name of the C subroutine generated which will return the
160 constants. The default is XS_SUBNAME. Child subroutines have
161 "_" and the name length appended, so constants with 10
162 character names would be in "constant_10" with the default
163 XS_SUBNAME.
164
166 Nicholas Clark <nick@ccl4.org> based on the code in "h2xs" by Larry
167 Wall and others
168perl v5.34.0 2021-10-18 ExtUtils::Constant(3pm)