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ExtUtils::Constant(3pm)Perl Programmers Reference GuideExtUtils::Constant(3pm)
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 mod-
ules 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 charac-
ters.
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 con-
stants 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 fol-
low 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_con-
stant" 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, 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 combina-
tion 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 expres-
sions 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-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 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 dif-
fer 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 "con-
stant_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 PACK-
AGE::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 sub-
routine "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 con-
stant 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 subrou-
tines 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 AT ccl4.org> based on the code in "h2xs" by Larry Wall and others
perl v5.8.6 2001-09-21 ExtUtils::Constant(3pm)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2008-11-22 06:45 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)