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 mod-
    ule_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.

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.

    -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; addi-
   tionally 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 struc-
   ture, initialised to zeroes.

    -b, --compat-version=version
   Generates a .pm file which is backwards compatible with the speci-
   fied 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.

    -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"-equiva-
   lent to integers may represent OS-related handles, and one may
   want to work with these handles in OO-way, as in "$han-
   dle->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_wild-
   card_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() func-
   tion and "sub AUTOLOAD" for constants.

    --skip-strict
   Do not use the pragma "strict".

    --skip-warnings
   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-edit-
   ing. 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

     # 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 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 pre-
    processor 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 direc-
   tory, 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.

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 parame-
    ter. 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_

   int
   foo(sv)
     SV *sv

    See perlxs and perlxstut for additional details.