ExtUtils::Constant - generate XS code to import C header constants

    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

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 CWh2xs utility, on which this code is based. It doesn't contain the routines to scan header files to extract these constants.

Generally one only needs to call the CWWriteConstants function, and then

    #include "const-c.inc"

in the C section of CWFoo.xs

    INCLUDE: const-xs.inc

in the XS section of CWFoo.xs.

For greater flexibility use CWconstant_types(), CWC_constant and CWXS_constant, with which CWWriteConstants 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 CWConfigure script at compile time.

IV

signed integer, at least 32 bits.

UV

unsigned integer, the same size as IV

NV

floating point type, probably CWdouble, possibly CWlong double

PV

NUL terminated string, length will be determined with CWstrlen

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. (CWPL_sv_yes) The value is not needed (and ignored).

NO

Defined Falsehood. (CWPL_sv_no) The value is not needed (and ignored).

UNDEF

CWundef. The value of the macro is not needed.

constant_types

A function returning a single scalar with CW#define definitions for the constants used internally between the generated C and XS functions.

XS_constant PACKAGE, TYPES, 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 CWC_constant, and usually named CWconstant. TYPES should be given either as a comma separated list of types that the C subroutine CWconstant will generate or as a reference to a hash. It should be the same list of types as CWC_constant was given. [Otherwise CWXS_constant and CWC_constant may have different ideas about the number of parameters passed to the C function CWconstant] You can call the perl visible subroutine something other than CWconstant if you give the parameter 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 CWWriteConstants, with the addition of CWINDENT to specify the number of leading spaces (default 2). Currently only CWINDENT, CWNAME, CWDEFAULT_TYPE, CWNAMES, CWC_FILE and CWXS_FILE are recognised.

WriteConstants ATTRIBUTE => VALUE [, ...]

Writes a file of C code and a file of XS code which you should CW#include and CWINCLUDE in the C and XS sections respectively of your module's XS code. You probably want to do this in your CWMakefile.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 CWIV 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.

C_FILE

The name of the file to write containing the C code. The default is CWconst-c.inc. The CW- 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 CW.c avoids having to override Makefile.PL's CW.xs to CW.c rules.

XS_FILE

The name of the file to write containing the XS code. The default is CWconst-xs.inc.

SUBNAME

The perl visible name of the XS subroutine generated which will return the constants. The default is CWconstant.

C_SUBNAME

The name of the C subroutine generated which will return the constants. The default is SUBNAME. Child subroutines have CW_ and the name length appended, so constants with 10 character names would be in CWconstant_10 with the default XS_SUBNAME.

Nicholas Clark <nick@ccl4.org> based on the code in CWh2xs by Larry Wall and others