ExtUtils::Constant - generate XS code to import C header constants

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

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; 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.
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_constant, 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, values being the hashrefs in the ITEM list. (No parameters 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 combination 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 generated, 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...; A function that returns a list of C subroutine definitions 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
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

AUTHOR

Nicholas Clark <nick@ccl4.org> based on the code in h2xs by Larry Wall and others

ExtUtils::Constant - generate XS code to import C header constants