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ExtUtils::Constant(3)
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.
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_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
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
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
"#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 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
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 "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
SUBNAME_LEN, for example "constant_5" for names 5 characters 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 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
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".
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 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 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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