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ExtUtils::Constant(3pm)Perl Programmers Reference GuideExtUtils::Constant(3pm)




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



perl v5.24.0                      2015-10-14           ExtUtils::Constant(3pm)

perl 5.24 - Generated Tue Nov 8 15:12:09 CST 2016
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