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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 argu-
       ments of the form -L/another/library/path in the extra-libraries argument.

       -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 argu-
            ment. 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

       -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 direc-

       -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 "type-
            def"-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()" mecha-

       -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 inte-
            ger).  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 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 declara-
            tions included from file NAME2.

            Note that some types of arguments/return-values for functions may result in XSUB-declara-
            tions/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

           # 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 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

       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.

       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 v5.8.8                       2012-01-22                           H2XS(1)