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