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_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
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.
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_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...; 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
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".; 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
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 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
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 <nick@ccl4.org> based on the code in "h2xs"
by Larry Wall and others

docs.sk

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