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Updated: July 2014

h2xs (1)


h2xs - convert .h C header files to Perl extensions


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

h2xs -h|-?|--help


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

     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

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          selects functions/macros to process.

     -O, --overwrite-ok
          Allows a pre-existing extension directory to be

     -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.

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     -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.

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Perl Programmers Reference Guide                          H2XS(1)

          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()" 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

          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
          constant() function and "sub AUTOLOAD" for constants.

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Perl Programmers Reference Guide                          H2XS(1)

          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.

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         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

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Perl Programmers Reference Guide                          H2XS(1)

     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 guess.

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

     No environment variables are used.

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Perl Programmers Reference Guide                          H2XS(1)

     Larry Wall and others

     See attributes(5) for descriptions of the following

     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
     perl, perlxstut, ExtUtils::MakeMaker, and AutoLoader.

     The usual warnings if it cannot read or write the files

     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

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Perl Programmers Reference Guide                          H2XS(1)

                 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.

     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

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