ExtUtils::Constant man page on aLinux

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ExtUtils::Constant(3)  Perl Programmers Reference Guide	 ExtUtils::Constant(3)

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, 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 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".

	   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".

	   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 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 v5.10.0			  2007-12-18		 ExtUtils::Constant(3)
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