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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_con-
       stant" 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
       C_stringify NAME
           A function which returns a 7 bit ASCII correctly \
           escaped version of the string passed suitable for C's
           "" or ''. It will die if passed Unicode characters.

       perl_stringify NAME
           A function which returns a 7 bit ASCII correctly \
           escaped version of the string passed suitable for a
           perl "" string.

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

       memEQ_clause NAME, CHECKED_AT, INDENT
           A function to return a suitable C "if" statement to
           check whether NAME is equal to the C variable "name".
           If CHECKED_AT is defined, then it is used to avoid
           "memEQ" for short names, or to generate a comment to
           highlight the position of the character in the
           "switch" statement.

           If CHECKED_AT is a reference to a scalar, then instead
           it gives the characters pre-checked at the beginning,
           (and the number of chars by which the C variable name
           has been advanced. These need to be chopped from the
           front of NAME).

       assign INDENT, TYPE, PRE, POST, VALUE...
           A function to return a suitable assignment clause. If
           TYPE is aggregate (eg PVN expects both pointer and
           length) then there should be multiple VALUEs for the
           components. PRE and POST if defined give snippets of C
           code to proceed and follow the assignment. PRE will be
           at the start of a block, so variables may be defined
           in it.

       return_clause
           return_clause ITEM, INDENT



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


           A function to return a suitable "#ifdef" clause. ITEM
           is a hashref (as passed to "C_constant" and
           "match_clause". INDENT is the number of spaces to
           indent, defaulting to 6.

           XXX document me

       switch_clause INDENT, NAMELEN, ITEMHASH, ITEM...
           An internal function to generate a suitable "switch"
           clause, called by "C_constant" ITEMs are in the hash
           ref format as given in the description of "C_con-
           stant", and must all have the names of the same
           length, given by NAMELEN (This is not checked).
           ITEMHASH is a reference to a hash, keyed by name, val-
           ues being the hashrefs in the ITEM list.  (No parame-
           ters are modified, and there can be keys in the
           ITEMHASH that are not in the list of ITEMs without
           causing problems).

       params WHAT
           An internal function. WHAT should be a hashref of
           types the constant function will return. params
           returns a hashref keyed IV NV PV SV to show which com-
           bination of pointers will be needed in the C argument
           list.

       dump_names
           dump_names DEFAULT_TYPE, TYPES, INDENT, OPTIONS,
           ITEM...

           An internal function to generate the embedded perl
           code that will regenerate the constant subroutines.
           DEFAULT_TYPE, TYPES and ITEMs are the same as for
           C_constant.  INDENT is treated as number of spaces to
           indent by.  OPTIONS is a hashref of options. Currently
           only "declare_types" is recognised.  If the value is
           true a $types is always declared in the perl code gen-
           erated, if defined and false never declared, and if
           undefined $types is only declared if the values in
           TYPES as passed in cannot be inferred from
           DEFAULT_TYPES and the ITEMs.

       dogfood
           dogfood PACKAGE, SUBNAME, DEFAULT_TYPE, TYPES, INDENT,
           BREAKOUT, ITEM...

           An internal function to generate the embedded perl
           code that will regenerate the constant subroutines.
           Parameters are the same as for C_constant.

       C_constant
           C_constant PACKAGE, SUBNAME, DEFAULT_TYPE, TYPES,
           INDENT, BREAKOUT, ITEM...




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           A function that returns a list of C subroutine defini-
           tions that return the value and type of constants when
           passed the name by the XS wrapper.  ITEM... gives a
           list of constant names. Each can either be a string,
           which is taken as a C macro name, or a reference to a
           hash with the following keys

           name    The name of the constant, as seen by the perl
                   code.

           type    The type of the constant (IV, NV etc)

           value   A C expression for the value of the constant,
                   or a list of C expressions if the type is
                   aggregate. This defaults to the name if not
                   given.

           macro   The C pre-processor macro to use in the
                   "#ifdef". This defaults to the name, and is
                   mainly used if value is an "enum". If a refer-
                   ence an array is passed then the first element
                   is used in place of the "#ifdef" line, and the
                   second element in place of the "#endif". This
                   allows pre-processor constructions such as

                       #if defined (foo)
                       #if !defined (bar)
                       ...
                       #endif
                       #endif

                   to be used to determine if a constant is to be
                   defined.

                   A "macro" 1 signals that the constant is
                   always defined, so the "#if"/"#endif" test is
                   omitted.

           default Default value to use (instead of "croak"ing
                   with "your vendor has not defined...") to
                   return if the macro isn't defined. Specify a
                   reference to an array with type followed by
                   value(s).

           pre     C code to use before the assignment of the
                   value of the constant. This allows you to use
                   temporary variables to extract a value from
                   part of a "struct" and return this as value.
                   This C code is places at the start of a block,
                   so you can declare variables in it.

           post    C code to place between the assignment of
                   value (to a temporary) and the return from the
                   function. This allows you to clear up anything



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                   in pre.  Rarely needed.

           def_pre =item def_post
                   Equivalents of pre and post for the default
                   value.

           utf8    Generated internally. Is zero or undefined if
                   name is 7 bit ASCII, "no" if the name is 8 bit
                   (and so should only match if SvUTF8() is
                   false), "yes" if the name is utf8 encoded.

                   The internals automatically clone any name
                   with characters 128-255 but none 256+ (ie one
                   that could be either in bytes or utf8) into a
                   second entry which is utf8 encoded.

           PACKAGE is the name of the package, and is only used
           in comments inside the generated C code.

           The next 5 arguments can safely be given as "undef",
           and are mainly used for recursion. SUBNAME defaults to
           "constant" if undefined.

           DEFAULT_TYPE is the type returned by "ITEM"s that
           don't specify their type. In turn it defaults to IV.
           TYPES should be given either as a comma separated list
           of types that the C subroutine "constant" will gener-
           ate or as a reference to a hash. DEFAULT_TYPE will be
           added to the list if not present, as will any types
           given in the list of ITEMs. The resultant list should
           be the same list of types that "XS_constant" is given.
           [Otherwise "XS_constant" and "C_constant" may differ
           in the number of parameters to the constant function.
           INDENT is currently unused and ignored. In future it
           may be used to pass in information used to change the
           C indentation style used.]  The best way to maintain
           consistency is to pass in a hash reference and let
           this function update it.

           BREAKOUT governs when child functions of SUBNAME are
           generated.  If there are BREAKOUT or more ITEMs with
           the same length of name, then the code to switch
           between them is placed into a function named SUB-
           NAME_LEN, for example "constant_5" for names 5 charac-
           ters long.  The default BREAKOUT is 3.  A single
           "ITEM" is always inlined.

       XS_constant PACKAGE, TYPES, SUBNAME, C_SUBNAME
           A function to generate the XS code to implement the
           perl subroutine PACKAGE::constant used by PACK-
           AGE::AUTOLOAD to load constants.  This XS code is a
           wrapper around a C subroutine usually generated by
           "C_constant", and usually named "constant".




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


           TYPES should be given either as a comma separated list
           of types that the C subroutine "constant" will gener-
           ate 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 SUB-
           NAME. 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 con-
           stant() 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 sup-
           ported 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



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               this number or more names in.

           NAMES
               An array of constants' names, either scalars con-
               taining names, or hashrefs as detailed in "C_con-
               stant".

           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 gener-
               ated 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_SUB-
               NAME.

AUTHOR
       Nicholas Clark <nickATccl4.org> based on the code in "h2xs"
       by Larry Wall and others






















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