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.\" ========================================================================
.\"
.IX Title "ExtUtils::Constant 3pm"
.TH ExtUtils::Constant 3pm "2023-05-18" "perl v5.26.3" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
ExtUtils::Constant \- generate XS code to import C header constants
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 7
\&    use ExtUtils::Constant qw (WriteConstants);
\&    WriteConstants(
\&        NAME => \*(AqFoo\*(Aq,
\&        NAMES => [qw(FOO BAR BAZ)],
\&    );
\&    # Generates wrapper code to make the values of the constants FOO BAR BAZ
\&    #  available to perl
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
ExtUtils::Constant facilitates generating C and \s-1XS\s0 wrapper code to allow
perl modules to \s-1AUTOLOAD\s0 constants defined in C library header files.
It is principally used by the \f(CW\*(C`h2xs\*(C'\fR utility, on which this code is based.
It doesn't contain the routines to scan header files to extract these
constants.
.SH "USAGE"
.IX Header "USAGE"
Generally one only needs to call the \f(CW\*(C`WriteConstants\*(C'\fR function, and then
.PP
.Vb 1
\&    #include "const\-c.inc"
.Ve
.PP
in the C section of \f(CW\*(C`Foo.xs\*(C'\fR
.PP
.Vb 1
\&    INCLUDE: const\-xs.inc
.Ve
.PP
in the \s-1XS\s0 section of \f(CW\*(C`Foo.xs\*(C'\fR.
.PP
For greater flexibility use \f(CW\*(C`constant_types()\*(C'\fR, \f(CW\*(C`C_constant\*(C'\fR and
\&\f(CW\*(C`XS_constant\*(C'\fR, with which \f(CW\*(C`WriteConstants\*(C'\fR is implemented.
.PP
Currently this module understands the following types. h2xs may only know
a subset. The sizes of the numeric types are chosen by the \f(CW\*(C`Configure\*(C'\fR
script at compile time.
.IP "\s-1IV\s0" 4
.IX Item "IV"
signed integer, at least 32 bits.
.IP "\s-1UV\s0" 4
.IX Item "UV"
unsigned integer, the same size as \fI\s-1IV\s0\fR
.IP "\s-1NV\s0" 4
.IX Item "NV"
floating point type, probably \f(CW\*(C`double\*(C'\fR, possibly \f(CW\*(C`long double\*(C'\fR
.IP "\s-1PV\s0" 4
.IX Item "PV"
\&\s-1NUL\s0 terminated string, length will be determined with \f(CW\*(C`strlen\*(C'\fR
.IP "\s-1PVN\s0" 4
.IX Item "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 \fI\s-1PV\s0\fR
.IP "\s-1SV\s0" 4
.IX Item "SV"
A \fBmortal\fR \s-1SV.\s0
.IP "\s-1YES\s0" 4
.IX Item "YES"
Truth.  (\f(CW\*(C`PL_sv_yes\*(C'\fR)  The value is not needed (and ignored).
.IP "\s-1NO\s0" 4
.IX Item "NO"
Defined Falsehood.  (\f(CW\*(C`PL_sv_no\*(C'\fR)  The value is not needed (and ignored).
.IP "\s-1UNDEF\s0" 4
.IX Item "UNDEF"
\&\f(CW\*(C`undef\*(C'\fR.  The value of the macro is not needed.
.SH "FUNCTIONS"
.IX Header "FUNCTIONS"
.IP "constant_types" 4
.IX Item "constant_types"
A function returning a single scalar with \f(CW\*(C`#define\*(C'\fR definitions for the
constants used internally between the generated C and \s-1XS\s0 functions.
.IP "XS_constant \s-1PACKAGE, TYPES, XS_SUBNAME, C_SUBNAME\s0" 4
.IX Item "XS_constant PACKAGE, TYPES, XS_SUBNAME, C_SUBNAME"
A function to generate the \s-1XS\s0 code to implement the perl subroutine
\&\fI\s-1PACKAGE\s0\fR::constant used by \fI\s-1PACKAGE\s0\fR::AUTOLOAD to load constants.
This \s-1XS\s0 code is a wrapper around a C subroutine usually generated by
\&\f(CW\*(C`C_constant\*(C'\fR, and usually named \f(CW\*(C`constant\*(C'\fR.
.Sp
\&\fI\s-1TYPES\s0\fR should be given either as a comma separated list of types that the
C subroutine \f(CW\*(C`constant\*(C'\fR will generate or as a reference to a hash. It should
be the same list of types as \f(CW\*(C`C_constant\*(C'\fR was given.
[Otherwise \f(CW\*(C`XS_constant\*(C'\fR and \f(CW\*(C`C_constant\*(C'\fR may have different ideas about
the number of parameters passed to the C function \f(CW\*(C`constant\*(C'\fR]
.Sp
You can call the perl visible subroutine something other than \f(CW\*(C`constant\*(C'\fR if
you give the parameter \fI\s-1XS_SUBNAME\s0\fR. The C subroutine it calls defaults to
the name of the perl visible subroutine, unless you give the parameter
\&\fIC_SUBNAME\fR.
.IP "autoload \s-1PACKAGE, VERSION, AUTOLOADER\s0" 4
.IX Item "autoload PACKAGE, VERSION, AUTOLOADER"
A function to generate the \s-1AUTOLOAD\s0 subroutine for the module \fI\s-1PACKAGE\s0\fR
\&\fI\s-1VERSION\s0\fR is the perl version the code should be backwards compatible with.
It defaults to the version of perl running the subroutine.  If \fI\s-1AUTOLOADER\s0\fR
is true, the \s-1AUTOLOAD\s0 subroutine falls back on AutoLoader::AUTOLOAD for all
names that the \fIconstant()\fR routine doesn't recognise.
.IP "WriteMakefileSnippet" 4
.IX Item "WriteMakefileSnippet"
WriteMakefileSnippet \s-1ATTRIBUTE\s0 => \s-1VALUE\s0 [, ...]
.Sp
A function to generate perl code for Makefile.PL that will regenerate
the constant subroutines.  Parameters are named as passed to \f(CW\*(C`WriteConstants\*(C'\fR,
with the addition of \f(CW\*(C`INDENT\*(C'\fR to specify the number of leading spaces
(default 2).
.Sp
Currently only \f(CW\*(C`INDENT\*(C'\fR, \f(CW\*(C`NAME\*(C'\fR, \f(CW\*(C`DEFAULT_TYPE\*(C'\fR, \f(CW\*(C`NAMES\*(C'\fR, \f(CW\*(C`C_FILE\*(C'\fR and
\&\f(CW\*(C`XS_FILE\*(C'\fR are recognised.
.IP "WriteConstants \s-1ATTRIBUTE\s0 => \s-1VALUE\s0 [, ...]" 4
.IX Item "WriteConstants ATTRIBUTE => VALUE [, ...]"
Writes a file of C code and a file of \s-1XS\s0 code which you should \f(CW\*(C`#include\*(C'\fR
and \f(CW\*(C`INCLUDE\*(C'\fR in the C and \s-1XS\s0 sections respectively of your module's \s-1XS\s0
code.  You probably want to do this in your \f(CW\*(C`Makefile.PL\*(C'\fR, so that you can
easily edit the list of constants without touching the rest of your module.
The attributes supported are
.RS 4
.IP "\s-1NAME\s0" 4
.IX Item "NAME"
Name of the module.  This must be specified
.IP "\s-1DEFAULT_TYPE\s0" 4
.IX Item "DEFAULT_TYPE"
The default type for the constants.  If not specified \f(CW\*(C`IV\*(C'\fR is assumed.
.IP "\s-1BREAKOUT_AT\s0" 4
.IX Item "BREAKOUT_AT"
The names of the constants are grouped by length.  Generate child subroutines
for each group with this number or more names in.
.IP "\s-1NAMES\s0" 4
.IX Item "NAMES"
An array of constants' names, either scalars containing names, or hashrefs
as detailed in \*(L"C_constant\*(R".
.IP "\s-1PROXYSUBS\s0" 4
.IX Item "PROXYSUBS"
If true, uses proxy subs. See ExtUtils::Constant::ProxySubs.
.IP "C_FH" 4
.IX Item "C_FH"
A filehandle to write the C code to.  If not given, then \fIC_FILE\fR is opened
for writing.
.IP "C_FILE" 4
.IX Item "C_FILE"
The name of the file to write containing the C code.  The default is
\&\f(CW\*(C`const\-c.inc\*(C'\fR.  The \f(CW\*(C`\-\*(C'\fR 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 \f(CW\*(C`.c\*(C'\fR avoids having to override Makefile.PL's
\&\f(CW\*(C`.xs\*(C'\fR to \f(CW\*(C`.c\*(C'\fR rules.
.IP "\s-1XS_FH\s0" 4
.IX Item "XS_FH"
A filehandle to write the \s-1XS\s0 code to.  If not given, then \fI\s-1XS_FILE\s0\fR is opened
for writing.
.IP "\s-1XS_FILE\s0" 4
.IX Item "XS_FILE"
The name of the file to write containing the \s-1XS\s0 code.  The default is
\&\f(CW\*(C`const\-xs.inc\*(C'\fR.
.IP "\s-1XS_SUBNAME\s0" 4
.IX Item "XS_SUBNAME"
The perl visible name of the \s-1XS\s0 subroutine generated which will return the
constants. The default is \f(CW\*(C`constant\*(C'\fR.
.IP "C_SUBNAME" 4
.IX Item "C_SUBNAME"
The name of the C subroutine generated which will return the constants.
The default is \fI\s-1XS_SUBNAME\s0\fR.  Child subroutines have \f(CW\*(C`_\*(C'\fR and the name
length appended, so constants with 10 character names would be in
\&\f(CW\*(C`constant_10\*(C'\fR with the default \fI\s-1XS_SUBNAME\s0\fR.
.RE
.RS 4
.RE
.SH "AUTHOR"
.IX Header "AUTHOR"
Nicholas Clark <nick@ccl4.org> based on the code in \f(CW\*(C`h2xs\*(C'\fR by Larry Wall and
others
