MirOS Manual: ExtUtils::Constant(3p)


ExtUtils::ConstanPerl)Programmers ReferenceExtUtils::Constant(3p)

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" func-
     tion, 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 imple-
     mented.

     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

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         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 usu-
         ally 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 [, ...]

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         A function to generate perl code for Makefile.PL that
         will regenerate the constant subroutines.  Parameters
         are named as passed to "WriteConstants", with the addi-
         tion 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 speci-
             fied "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 con-
             taining names, or hashrefs as detailed in
             "C_constant".

         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_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

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             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

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