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 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.

       -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 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 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

                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

       -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

       -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

            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.

            When --compat-version (-b) is present the generated tests will use
            "Test::More" rather than "Test" which is the default for versions
            before 5.6.2.  "Test::More" will be added to PREREQ_PM in the
            generated "Makefile.PL".

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

            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 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".

           # 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 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 OK.

       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 guess.

           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 v5.30.3                       2021-11-13                            H2XS(1)