ExtUtils::Constant - generate XS code to import C header constants
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
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.
Generally one only needs to call the
WriteConstants function, and then
in the C section of
in the XS section of
For greater flexibility use
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.
signed integer, at least 32 bits.
unsigned integer, the same size as IV
floating point type, probably
NUL terminated string, length will be determined with
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
A mortal SV.
PL_sv_yes) The value is not needed (and ignored).
Defined Falsehood. (
PL_sv_no) The value is not needed (and ignored).
undef. The value of the macro is not needed.
A function which returns a correctly \ escaped version of the string passed suitable for C's "" or ''. It will also be valid as a perl "" string.
A function returning a single scalar with
#define definitions for the constants used internally between the generated C and XS functions.
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
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 preceed and follow the assignment. PRE will be at the start of a block, so variables may be defined in it.
return_clause VALUE, TYPE, INDENT, MACRO, DEFAULT, PRE, POST, PRE, POST
A function to return a suitable
#ifdef clause. MACRO defaults to VALUE when not defined. If TYPE is aggregate (eg PVN expects both pointer and length) then VALUE should be a reference to an array of values in the order expected by the type.
C_constant will always call this function with MACRO defined, defaulting to the constant's name. DEFAULT if defined is an array reference giving default type and value(s) if the clause generated by MACRO doesn't evaluate to true. The two pairs PRE and POST if defined give C code snippets to proceed and follow the value, and the default value.
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).
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 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 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 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
The name of the constant, as seen by the perl code.
The type of the constant (IV, NV etc)
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.
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 reference 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
#endif test is omitted.
Default value to use (instead of
croaking 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).
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.
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 in pre. Rarely needed.
Equivalents of pre and post for the default value.
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
ITEMs 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 generate 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
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 SUBNAME_LEN, for example
constant_5 for names 5 characters long. The default BREAKOUT is 3. A single
ITEM is always inlined.
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
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
C_constant may have different ideas about the number of parameters passed to the C function
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.
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 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).
XS_FILE are recognised.
Writes a file of C code and a file of XS code which you should
INCLUDE in the C and XS sections respectively of your module's XS code. You probaby 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 of the module. This must be specified
The default type for the constants. If not specified
IV is assumed.
The names of the constants are grouped by length. Generate child subroutines for each group with this number or more names in.
An array of constants' names, either scalars containing names, or hashrefs as detailed in "C_constant".
The name of the file to write containing the C code. The default is
- 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
The name of the file to write containing the XS code. The default is
The perl visible name of the XS subroutine generated which will return the constants. The default is
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.
Nicholas Clark <email@example.com> based on the code in
h2xs by Larry Wall and others