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NAME    [Toc]    [Back]

       h2xs - convert .h C header files to Perl extensions

SYNOPSIS    [Toc]    [Back]

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

       h2xs -h|-?|--help

DESCRIPTION    [Toc]    [Back]

       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

       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.

OPTIONS    [Toc]    [Back]

       -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 templates for
            a module which is not XS-based.  "-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

       -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

       -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.

            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()"

       -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 5.7.2 .
            "Test::More" will be added to PREREQ_PM in the generated

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

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

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

            Do not use the module "AutoLoader"; but keep the con-
            stant() 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".

EXAMPLES    [Toc]    [Back]

           # Default behavior, extension is Rusers
           h2xs rpcsvc/rusers

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

           #    Extension    is   rpcsvc::rusers.   Still   finds
           h2xs rpcsvc::rusers

           #    Extension    is    ONC::RPC.      Still     finds
           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  Lib::Foo  which  works at least with
           # 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
           # Constants are created for all #defines but only  for
           # 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
           h2xs -n DCE::rgynbase -p sec_rgy_ dce/rgynbase

           # Extension is DCE::rgynbase
           # prefix "sec_rgy_"  is  dropped  from  perl  function
           #  subroutines  are  created for sec_rgy_wildcard_name
           # 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
           # visible from perl.h. Name of the extension is perl1.
           #  When  scanning  perl.h, define -DEXT=extern -DdEXT=
           # 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="

           # 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 accessable
 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

       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

       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

       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

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

ENVIRONMENT    [Toc]    [Back]

       No environment variables are used.

AUTHOR    [Toc]    [Back]

       Larry Wall and others

SEE ALSO    [Toc]    [Back]

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

DIAGNOSTICS    [Toc]    [Back]

       The usual warnings if it cannot read or write the files

LIMITATIONS of -x    [Toc]    [Back]

       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

               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 v5.8.5                 2002-11-06                          9
[ Back ]
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