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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 supplied then the name of the first
     header file will be used, with the first character capital-
     ized.

     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 aug-
     mented by including arguments of the form
     -L/another/library/path in the extra-libraries argument.

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 declarations.  Writes
	  these options in the generated Makefile.PL too.

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

     -O, --overwrite-ok


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	  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 templates for a
	  module which is not XS-based.	 "-c" and "-f" are impli-
	  citly 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 facili-
	  tate chained calls.

	  These methods all apply to the Ptr type for the struc-
	  ture; 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 ver-
	  sion of perl you are using to run h2xs will have no
	  effect.  If unspecified h2xs will default to compati-
	  bility 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

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	  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 argu-
	  ments 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 direc-
	  tories.

     -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 variable of the same name magi-
	  cally 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-

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	  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 ver-
	  sions 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 con-
	  stant() function and "sub AUTOLOAD" for constants.

     --skip-strict


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	  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 ver-
	  sion 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 con-
	  verted from/to a pointer (like "long long"), pointers
	  to functions, or arrays.  See also the section on "LIM-
	  ITATIONS 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

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	 # 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 func-
     tionality, and the corresponding header files.  How to
     create an extension which makes this functionality accessi-
     ble 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".

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     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 direc-
	 tories.  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 exten-
	 sion 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 auto-
	 generated 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

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

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 func-
     tion which is of the form, say, "int *", is an input, out-
     put, or input/output parameter.  In particular, argument
     declarations 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 func-
     tion

	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

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

	 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.

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