


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"
       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



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


           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



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


           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.





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


           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





































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