


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 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.

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.



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       -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



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            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 variable 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 "typedef"ed
            types as opaque types.



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            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.

       --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".




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       -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".

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.



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           # 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



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           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.




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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 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
       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_




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           int
           foo(sv)
               SV *sv

       See perlxs and perlxstut for additional details.




















































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