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

NAME
       h2xs - convert .h C header files to Perl extensions

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

       h2xs -h|-?|--help

DESCRIPTION
       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 sup-
       plied then the name of the first header file will be used, with the first character capi-
       talized.

       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.

OPTIONS
       -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 dec-
	    larations.	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 ele-
	    ment 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 enu-
	    meration. 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 option.

       -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 vari-
	    able of the same name magically tied to the C variable.

       -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 "type-
	    def"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 con-
	    stant() 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.

       --use-new-tests
	    When --compat-version (-b) is present the generated tests will use "Test::More"
	    rather than "Test" which is the default for versions before 5.7.2 .   "Test::More"
	    will be added to PREREQ_PM in the generated "Makefile.PL".

       --use-old-tests
	    Will force the generation of test code that uses the older "Test" module.

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

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

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

       --skip-strict
	    Do not use the pragma "strict".

       --skip-warnings
	    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 speci-
	    fied 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-dec-
	    larations/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".

EXAMPLES
	   # 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 inter-
       face_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
	     make test

       Hints
	   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.

ENVIRONMENT
       No environment variables are used.

AUTHOR
       Larry Wall and others

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

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

LIMITATIONS of -x
       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 declara-
       tions of the form

	   int
	   foo(n)
	       int *n

       should be better rewritten as

	   int
	   foo(n)
	       int &n

       if "n" is an input parameter.

       Additionally, h2xs has no facilities to intuit that a function

	  int
	  foo(addr,l)
	       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

	   int
	   foo(sv)
		   SV *addr
	       PREINIT:
		   STRLEN len;
		   char *s;
	       CODE:
		   s = SvPV(sv,len);
		   RETVAL = foo(s, len);
	       OUTPUT:
		   RETVAL

       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_

	   int
	   foo(sv)
	       SV *sv

       See perlxs and perlxstut for additional details.

perl v5.8.9				    2009-04-13					  H2XS(1)
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