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 perlExtUtils::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.
Memory footprint and run-time performance is not as good as specialized perfect hashes as with XSConfig or Win32::GUI::Constants.
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.incin 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.
signed integer, at least 32 bits.
unsigned integer, the same size as IV
floating point type, probably double, possibly long double
NUL terminated string, length will be determined with strlen
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.
Truth. (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 returning a single scalar with #define definitions for the constants used internally between the generated C and XS functions.
A function to generate the C code in const-c.inc to implement the perl subroutine PACKAGE::constant.
The $what paramater 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 XS_constant was given. Otherwise XS_constant and C_constant may have different ideas about the number of parameters passed to the C function constant.
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 XS_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.
This is needed unless you use PROXYSUBS = {autoload=>1}>, but which generates code unusable earlier than 5.8.
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.
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
NAMEName of the module. This must be specified
DEFAULT_TYPEThe default type for the constants. If not specified IV is assumed.
BREAKOUT_ATThe names of the constants are grouped by length. Generate child subroutines for each group with this number or more names in.
NAMESAn array of constants' names, either scalars containing names, or hashrefs as detailed in "C_constant".
PROXYSUBSIf true, uses proxy subs. See ExtUtils::Constant::ProxySubs. PROXYSUBS create CONSTSUB's for each defined constant upfront, while without PROXYSUBS every constant is looked up at run-time. Thus it trades memory footprint for faster run-time performance.
Options: autoload, push, croak_on_error or croak_on_read with most of the options being exclusive, and croak_on_read usable since 5.24.
C_FHA filehandle to write the C code to. If not given, then C_FILE is opened for writing.
C_FILEThe 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_FHA filehandle to write the XS code to. If not given, then XS_FILE is opened for writing.
XS_FILEThe name of the file to write containing the XS code. The default is const-xs.inc.
XS_SUBNAMEThe perl visible name of the XS subroutine generated which will return the constants. The default is constant.
C_SUBNAMEThe name of the C subroutine generated which will return the constants. The default is XS_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.
You can calculate simple performance numbers with perl -Mblib t/Constant.t --bench --memtest /dev/null 2>bench.lst> and grep ^# bench.lst for 19 constants.
Option Memory [b] Time [s]
<none> 1612758 0.023946
PROXYSUBS 1593553 0.020061
PROXYSUBS autoload 1588555 0.024906
PROXYSUBS push 1608709 0.023361
PROXYSUBS
croak_on_error 1590267 0.023052
PROXYSUBS
croak_on_read 1599747 0.021710
PROXYSUBS
autoload push 1589737 0.021917
PROXYSUBS
croak_on_error push 1590606 0.021669PROXYSUBS without any option is the fastest, and on the lower side of memory.
PROXYSUBS autoload is the slowest, but easiest to use.
The old method without PROXYSUBS uses the most memory and is 2nd slowest.
With >500 constants:
Option Memory [b] Time [s]
<none> 2572650 0.025867
PROXYSUBS 2145701 0.024928
PROXYSUBS autoload 2133418 0.024154
PROXYSUBS push 2173807 0.030029
PROXYSUBS
croak_on_error 2142773 0.025776
PROXYSUBS
croak_on_read 2144780 0.027649
PROXYSUBS
autoload push 2161453 0.026092
PROXYSUBS
croak_on_error push 2170791 0.027433There are no numbers compared to perfect hashes yet. The estimation is that EU-C is ~50% slower and bigger, as seen with Win32::GUI::Constants and XSConfig. See also Perfect::Hash.
Reini Urban <rurban@cpan.org> fixed up ProxySubs and took over maintainance. Nicholas Clark <nick@ccl4.org> wrote it based on the code in h2xs by Larry Wall and others.