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H2XS(1)		       Perl Programmers	Reference Guide		       H2XS(1)

       h2xs - convert .h C header files	to Perl	extensions

       h2xs [OPTIONS ...] [headerfile ... [extra_libraries]]

       h2xs -h|-?|--help

       h2xs builds a Perl extension from C header files.  The extension	will
       include functions which can be used to retrieve the value of any
       #define statement which was in the C header files.

       The module_name will be used for	the name of the	extension.  If
       module_name is not supplied then	the name of the	first header file will
       be used,	with the first character capitalized.

       If the extension	might need extra libraries, they should	be included
       here.  The extension Makefile.PL	will take care of checking whether the
       libraries actually exist	and how	they should be loaded.	The extra
       libraries should	be specified in	the form -lm -lposix, etc, just	as on
       the cc command line.  By	default, the Makefile.PL will search through
       the library path	determined by Configure.  That path can	be augmented
       by including arguments of the form -L/another/library/path in the
       extra-libraries argument.

       In spite	of its name, h2xs may also be used to create a skeleton	pure
       Perl module. See	the -X option.

       -A, --omit-autoload
	    Omit all autoload facilities.  This	is the same as -c but also
	    removes the	"use AutoLoader" statement from	the .pm	file.

       -B, --beta-version
	    Use	an alpha/beta style version number.  Causes version number to
	    be "0.00_01" unless	-v is specified.

       -C, --omit-changes
	    Omits creation of the Changes file,	and adds a HISTORY section to
	    the	POD template.

       -F, --cpp-flags=addflags
	    Additional flags to	specify	to C preprocessor when scanning	header
	    for	function declarations.	Writes these options in	the generated
	    Makefile.PL	too.

       -M, --func-mask=regular expression
	    selects functions/macros to	process.

       -O, --overwrite-ok
	    Allows a pre-existing extension directory to be overwritten.

       -P, --omit-pod
	    Omit the autogenerated stub	POD section.

       -X, --omit-XS
	    Omit the XS	portion. Used to generate a skeleton pure Perl module.
	    "-c" and "-f" are implicitly enabled.

       -a, --gen-accessors
	    Generate an	accessor method	for each element of structs and
	    unions. The	generated methods are named after the element name;
	    will return	the current value of the element if called without
	    additional arguments; and will set the element to the supplied
	    value (and return the new value) if	called with an additional
	    argument. Embedded structures and unions are returned as a pointer
	    rather than	the complete structure,	to facilitate chained calls.

	    These methods all apply to the Ptr type for	the structure;
	    additionally two methods are constructed for the structure type
	    itself, "_to_ptr" which returns a Ptr type pointing	to the same
	    structure, and a "new" method to construct and return a new
	    structure, initialised to zeroes.

       -b, --compat-version=version
	    Generates a	.pm file which is backwards compatible with the
	    specified perl version.

	    For	versions < 5.6.0, the changes are.
		- no use of 'our' (uses	'use vars' instead)
		- no 'use warnings'

	    Specifying a compatibility version higher than the version of perl
	    you	are using to run h2xs will have	no effect.  If unspecified
	    h2xs will default to compatibility with the	version	of perl	you
	    are	using to run h2xs.

       -c, --omit-constant
	    Omit "constant()" from the .xs file	and corresponding specialised
	    "AUTOLOAD" from the	.pm file.

       -d, --debugging
	    Turn on debugging messages.

       -e, --omit-enums=[regular expression]
	    If regular expression is not given,	skip all constants that	are
	    defined in a C enumeration.	Otherwise skip only those constants
	    that are defined in	an enum	whose name matches regular expression.

	    Since regular expression is	optional, make sure that this switch
	    is followed	by at least one	other switch if	you omit regular
	    expression and have	some pending arguments such as header-file
	    names. This	is ok:

		h2xs -e	-n Module::Foo foo.h

	    This is not	ok:

		h2xs -n	Module::Foo -e foo.h

	    In the latter, foo.h is taken as regular expression.

       -f, --force
	    Allows an extension	to be created for a header even	if that	header
	    is not found in standard include directories.

       -g, --global
	    Include code for safely storing static data	in the .xs file.
	    Extensions that do no make use of static data can ignore this

       -h, -?, --help
	    Print the usage, help and version for this h2xs and	exit.

       -k, --omit-const-func
	    For	function arguments declared as "const",	omit the const
	    attribute in the generated XS code.

       -m, --gen-tied-var
	    Experimental: for each variable declared in	the header file(s),
	    declare a perl variable of the same	name magically tied to the C

       -n, --name=module_name
	    Specifies a	name to	be used	for the	extension, e.g., -n RPC::DCE

       -o, --opaque-re=regular expression
	    Use	"opaque" data type for the C types matched by the regular
	    expression,	even if	these types are	"typedef"-equivalent to	types
	    from typemaps.  Should not be used without -x.

	    This may be	useful since, say, types which are
	    "typedef"-equivalent to integers may represent OS-related handles,
	    and	one may	want to	work with these	handles	in OO-way, as in
	    "$handle->do_something()".	Use "-o	." if you want to handle all
	    the	"typedef"ed types as opaque types.

	    The	type-to-match is whitewashed (except for commas, which have no
	    whitespace before them, and	multiple "*" which have	no whitespace
	    between them).

       -p, --remove-prefix=prefix
	    Specify a prefix which should be removed from the Perl function
	    names, e.g., -p sec_rgy_ This sets up the XS PREFIX	keyword	and
	    removes the	prefix from functions that are autoloaded via the
	    "constant()" mechanism.

       -s, --const-subs=sub1,sub2
	    Create a perl subroutine for the specified macros rather than
	    autoload with the constant() subroutine.  These macros are assumed
	    to have a return type of char *, e.g.,
	    -s sec_rgy_wildcard_name,sec_rgy_wildcard_sid.

       -t, --default-type=type
	    Specify the	internal type that the constant() mechanism uses for
	    macros.  The default is IV (signed integer).  Currently all	macros
	    found during the header scanning process will be assumed to	have
	    this type.	Future versions	of "h2xs" may gain the ability to make
	    educated guesses.

	    When --compat-version (-b) is present the generated	tests will use
	    "Test::More" rather	than "Test" which is the default for versions
	    before 5.6.2.  "Test::More"	will be	added to PREREQ_PM in the
	    generated "Makefile.PL".

	    Will force the generation of test code that	uses the older "Test"

	    Do not use "Exporter" and/or export	any symbol.

	    Do not use "Devel::PPPort":	no portability to older	version.

	    Do not use the module "AutoLoader";	but keep the constant()
	    function and "sub AUTOLOAD"	for constants.

	    Do not use the pragma "strict".

	    Do not use the pragma "warnings".

       -v, --version=version
	    Specify a version number for this extension.  This version number
	    is added to	the templates.	The default is 0.01, or	0.00_01	if
	    "-B" is specified.	The version specified should be	numeric.

       -x, --autogen-xsubs
	    Automatically generate XSUBs basing	on function declarations in
	    the	header file.  The package "C::Scan" should be installed. If
	    this option	is specified, the name of the header file may look
	    like "NAME1,NAME2".	In this	case NAME1 is used instead of the
	    specified string, but XSUBs	are emitted only for the declarations
	    included from file NAME2.

	    Note that some types of arguments/return-values for	functions may
	    result in XSUB-declarations/typemap-entries	which need hand-
	    editing. Such may be objects which cannot be converted from/to a
	    pointer (like "long	long"),	pointers to functions, or arrays.  See
	    also the section on	"LIMITATIONS of	-x".

	   # Default behavior, extension is Rusers
	   h2xs	rpcsvc/rusers

	   # Same, but extension is RUSERS
	   h2xs	-n RUSERS rpcsvc/rusers

	   # Extension is rpcsvc::rusers. Still	finds <rpcsvc/rusers.h>
	   h2xs	rpcsvc::rusers

	   # Extension is ONC::RPC.  Still finds <rpcsvc/rusers.h>
	   h2xs	-n ONC::RPC rpcsvc/rusers

	   # Without constant()	or AUTOLOAD
	   h2xs	-c rpcsvc/rusers

	   # Creates templates for an extension	named RPC
	   h2xs	-cfn RPC

	   # Extension is ONC::RPC.
	   h2xs	-cfn ONC::RPC

	   # Extension is a pure Perl module with no XS	code.
	   h2xs	-X My::Module

	   # Extension is Lib::Foo which works at least	with Perl5.005_03.
	   # Constants are created for all #defines and	enums h2xs can find
	   # in	foo.h.
	   h2xs	-b 5.5.3 -n Lib::Foo foo.h

	   # Extension is Lib::Foo which works at least	with Perl5.005_03.
	   # Constants are created for all #defines but	only for enums
	   # whose names do not	start with 'bar_'.
	   h2xs	-b 5.5.3 -e '^bar_' -n Lib::Foo	foo.h

	   # Makefile.PL will look for library -lrpc in
	   # additional	directory /opt/net/lib
	   h2xs	rpcsvc/rusers -L/opt/net/lib -lrpc

	   # Extension is DCE::rgynbase
	   # prefix "sec_rgy_" is dropped from perl function names
	   h2xs	-n DCE::rgynbase -p sec_rgy_ dce/rgynbase

	   # Extension is DCE::rgynbase
	   # prefix "sec_rgy_" is dropped from perl function names
	   # subroutines are created for sec_rgy_wildcard_name and
	   # sec_rgy_wildcard_sid
	   h2xs	-n DCE::rgynbase -p sec_rgy_ \
	   -s sec_rgy_wildcard_name,sec_rgy_wildcard_sid dce/rgynbase

	   # Make XS without defines in	perl.h,	but with function declarations
	   # visible from perl.h. Name of the extension	is perl1.
	   # When scanning perl.h, define -DEXT=extern -DdEXT= -DINIT(x)=
	   # Extra backslashes below because the string	is passed to shell.
	   # Note that a directory with	perl header files would
	   #  be added automatically to	include	path.
	   h2xs	-xAn perl1 -F "-DEXT=extern -DdEXT= -DINIT\(x\)=" perl.h

	   # Same with function	declaration in proto.h as visible from perl.h.
	   h2xs	-xAn perl2 perl.h,proto.h

	   # Same but select only functions which match	/^av_/
	   h2xs	-M '^av_' -xAn perl2 perl.h,proto.h

	   # Same but treat SV*	etc as "opaque"	types
	   h2xs	-o '^[S]V \*$' -M '^av_' -xAn perl2 perl.h,proto.h

   Extension based on .h and .c	files
       Suppose that you	have some C files implementing some functionality, and
       the corresponding header	files.	How to create an extension which makes
       this functionality accessible in	Perl?  The example below assumes that
       the header files	are interface_simple.h and interface_hairy.h, and you
       want the	perl module be named as	"Ext::Ension".	If you need some
       preprocessor directives and/or linking with external libraries, see the
       flags "-F", "-L"	and "-l" in "OPTIONS".

       Find the	directory name
	   Start with a	dummy run of h2xs:

	     h2xs -Afn Ext::Ension

	   The only purpose of this step is to create the needed directories,
	   and let you know the	names of these directories.  From the output
	   you can see that the	directory for the extension is Ext/Ension.

       Copy C files
	   Copy	your header files and C	files to this directory	Ext/Ension.

       Create the extension
	   Run h2xs, overwriting older autogenerated files:

	     h2xs -Oxan	Ext::Ension interface_simple.h interface_hairy.h

	   h2xs	looks for header files after changing to the extension
	   directory, so it will find your header files	OK.

       Archive and test
	   As usual, run

	     cd	Ext/Ension
	     perl Makefile.PL
	     make dist
	     make test

	   It is important to do "make dist" as	early as possible.  This way
	   you can easily merge(1) your	changes	to autogenerated files if you
	   decide to edit your ".h" files and rerun h2xs.

	   Do not forget to edit the documentation in the generated .pm	file.

	   Consider the	autogenerated files as skeletons only, you may invent
	   better interfaces than what h2xs could guess.

	   Consider this section as a guideline	only, some other options of
	   h2xs	may better suit	your needs.

       No environment variables	are used.

       Larry Wall and others

       perl, perlxstut,	ExtUtils::MakeMaker, and AutoLoader.

       The usual warnings if it	cannot read or write the files involved.

       h2xs would not distinguish whether an argument to a C function which is
       of the form, say, "int *", is an	input, output, or input/output
       parameter.  In particular, argument declarations	of the form

	       int *n

       should be better	rewritten as

	       int &n

       if "n" is an input parameter.

       Additionally, h2xs has no facilities to intuit that a function

	       char *addr
	       int   l

       takes a pair of address and length of data at this address, so it is
       better to rewrite this function as

		   SV *addr
		   STRLEN len;
		   char	*s;
		   s = SvPV(sv,len);
		   RETVAL = foo(s, len);

       or alternately

	   static int
	   my_foo(SV *sv)
	       STRLEN len;
	       char *s = SvPV(sv,len);

	       return foo(s, len);

	   MODULE = foo	       PACKAGE = foo   PREFIX =	my_

	       SV *sv

       See perlxs and perlxstut	for additional details.

perl v5.28.3			  2021-03-01			       H2XS(1)


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