ExtUti...nstant(3perl) Perl Programmers Reference Guide ExtUti...nstant(3perl)
NAME
ExtUtils::Constant - generate XS code to import C header constants
SYNOPSIS
use ExtUtils::Constant qw (WriteConstants);
WriteConstants(
NAME => 'Foo',
NAMES => [qw(FOO BAR BAZ)],
);
# Generates wrapper code to make the values of the constants FOO BAR BAZ
# available to perl
DESCRIPTION
ExtUtils::Constant facilitates generating C and XS wrapper code to allow
perl modules to AUTOLOAD constants defined in C library header files.
It is principally used by the "h2xs" utility, on which this code is
based. It doesn't contain the routines to scan header files to extract
these constants.
USAGE
Generally one only needs to call the "WriteConstants" function, and then
#include "const-c.inc"
in the C section of "Foo.xs"
INCLUDE: const-xs.inc
in the XS section of "Foo.xs".
For greater flexibility use constant_types(), "C_constant" and
"XS_constant", with which "WriteConstants" is implemented.
Currently this module understands the following types. h2xs may only
know a subset. The sizes of the numeric types are chosen by the
"Configure" script at compile time.
IV signed integer, at least 32 bits.
UV unsigned integer, the same size as IV
NV floating point type, probably "double", possibly "long double"
PV NUL terminated string, length will be determined with "strlen"
PVN A fixed length thing, given as a [pointer, length] pair. If you know
the length of a string at compile time you may use this instead of
PV
SV A mortal SV.
YES Truth. ("PL_sv_yes") The value is not needed (and ignored).
NO Defined Falsehood. ("PL_sv_no") The value is not needed (and
ignored).
UNDEF
"undef". The value of the macro is not needed.
FUNCTIONS
constant_types
A function returning a single scalar with "#define" definitions for
the constants used internally between the generated C and XS
functions.
XS_constant PACKAGE, TYPES, XS_SUBNAME, C_SUBNAME
A function to generate the XS code to implement the perl subroutine
PACKAGE::constant used by PACKAGE::AUTOLOAD to load constants. This
XS code is a wrapper around a C subroutine usually generated by
"C_constant", and usually named "constant".
TYPES should be given either as a comma separated list of types that
the C subroutine "constant" will generate or as a reference to a
hash. It should be the same list of types as "C_constant" was given.
[Otherwise "XS_constant" and "C_constant" may have different ideas
about the number of parameters passed to the C function "constant"]
You can call the perl visible subroutine something other than
"constant" if you give the parameter XS_SUBNAME. The C subroutine it
calls defaults to the name of the perl visible subroutine, unless
you give the parameter C_SUBNAME.
autoload PACKAGE, VERSION, AUTOLOADER
A function to generate the AUTOLOAD subroutine for the module
PACKAGE VERSION is the perl version the code should be backwards
compatible with. It defaults to the version of perl running the
subroutine. If AUTOLOADER is true, the AUTOLOAD subroutine falls
back on AutoLoader::AUTOLOAD for all names that the constant()
routine doesn't recognise.
WriteMakefileSnippet
WriteMakefileSnippet ATTRIBUTE => VALUE [, ...]
A function to generate perl code for Makefile.PL that will
regenerate the constant subroutines. Parameters are named as passed
to "WriteConstants", with the addition of "INDENT" to specify the
number of leading spaces (default 2).
Currently only "INDENT", "NAME", "DEFAULT_TYPE", "NAMES", "C_FILE"
and "XS_FILE" are recognised.
WriteConstants ATTRIBUTE => VALUE [, ...]
Writes a file of C code and a file of XS code which you should
"#include" and "INCLUDE" in the C and XS sections respectively of
your module's XS code. You probably want to do this in your
"Makefile.PL", so that you can easily edit the list of constants
without touching the rest of your module. The attributes supported
are
NAME
Name of the module. This must be specified
DEFAULT_TYPE
The default type for the constants. If not specified "IV" is
assumed.
BREAKOUT_AT
The names of the constants are grouped by length. Generate
child subroutines for each group with this number or more names
in.
NAMES
An array of constants' names, either scalars containing names,
or hashrefs as detailed in "C_constant".
PROXYSUBS
If true, uses proxy subs. See ExtUtils::Constant::ProxySubs.
C_FH
A filehandle to write the C code to. If not given, then C_FILE
is opened for writing.
C_FILE
The name of the file to write containing the C code. The
default is "const-c.inc". The "-" in the name ensures that the
file can't be mistaken for anything related to a legitimate perl
package name, and not naming the file ".c" avoids having to
override Makefile.PL's ".xs" to ".c" rules.
XS_FH
A filehandle to write the XS code to. If not given, then
XS_FILE is opened for writing.
XS_FILE
The name of the file to write containing the XS code. The
default is "const-xs.inc".
XS_SUBNAME
The perl visible name of the XS subroutine generated which will
return the constants. The default is "constant".
C_SUBNAME
The name of the C subroutine generated which will return the
constants. The default is XS_SUBNAME. Child subroutines have
"_" and the name length appended, so constants with 10 character
names would be in "constant_10" with the default XS_SUBNAME.
AUTHOR
Nicholas Clark <nick@ccl4.org> based on the code in "h2xs" by Larry Wall
and others
perl v5.40.1 2026-08-30 ExtUti...nstant(3perl)
Generated by dwww version 1.16 on Sat Oct 3 07:43:34 CEST 2026.