ExtUtils::Constant
ExtUtils::Constant(3) Perl Programmers Reference Guide 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 "Con-
figure" 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 func-
tions.
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 assign-
ment. 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 con-
stant 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 refer-
ence 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 sec-
ond element in place of the "#endif". This allows pre-pro-
cessor 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 ven-
dor 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 tem-
porary) 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_con-
stant" may differ in the number of parameters to the constant func-
tion. 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 differ-
ent ideas about the number of parameters passed to the C function
"constant"]
You can call the perl visible subroutine something other than "con-
stant" 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 PACK-
AGE VERSION is the perl version the code should be backwards com-
patible with. It defaults to the version of perl running the sub-
routine. 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 regener-
ate the constant subroutines. Parameters are named as passed to
"WriteConstants", with the addition of "INDENT" to specify the num-
ber 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 "Make-
file.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
perl v5.8.6 2001-09-21 ExtUtils::Constant(3)
