H2XS(1) Perl Programmers Reference Guide H2XS(1)
h2xs - convert .h C header files to Perl extensions
h2xs [OPTIONS ...] [headerfile ... [extra_libraries]]
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
The module_name will be used for the name of the extension. If module_name is not sup-
plied then the name of the first header file will be used, with the first character capi-
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.
Omit all autoload facilities. This is the same as -c but also removes the
"use AutoLoader" statement from the .pm file.
Use an alpha/beta style version number. Causes version number to be "0.00_01" unless
-v is specified.
Omits creation of the Changes file, and adds a HISTORY section to the POD template.
Additional flags to specify to C preprocessor when scanning header for function dec-
larations. Writes these options in the generated Makefile.PL too.
-M, --func-mask=regular expression
selects functions/macros to process.
Allows a pre-existing extension directory to be overwritten.
Omit the autogenerated stub POD section.
Omit the XS portion. Used to generate templates for a module which is not XS-based.
"-c" and "-f" are implicitly enabled.
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 ele-
ment 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.
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.
Omit "constant()" from the .xs file and corresponding specialised "AUTOLOAD" from the
Turn on debugging messages.
Allows an extension to be created for a header even if that header is not found in
standard include directories.
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.
For function arguments declared as "const", omit the const attribute in the generated
Experimental: for each variable declared in the header file(s), declare a perl vari-
able of the same name magically tied to the C variable.
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
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 "type-
def"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).
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.
Create a perl subroutine for the specified macros rather than autoload with the con-
stant() subroutine. These macros are assumed to have a return type of char *, e.g.,
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 "Makefile.PL".
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".
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 speci-
fied should be numeric.
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
Note that some types of arguments/return-values for functions may result in XSUB-dec-
larations/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
# Same, but extension is RUSERS
h2xs -n RUSERS rpcsvc/rusers
# Extension is rpcsvc::rusers. Still finds <rpcsvc/rusers.h>
# 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 inter-
face_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
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
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
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.
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 parameter. In particular, argument declara-
tions of the form
should be better rewritten as
if "n" is an input parameter.
Additionally, h2xs has no facilities to intuit that a function
takes a pair of address and length of data at this address, so it is better to rewrite
this function as
s = SvPV(sv,len);
RETVAL = foo(s, len);
char *s = SvPV(sv,len);
return foo(s, len);
MODULE = foo PACKAGE = foo PREFIX = my_
See perlxs and perlxstut for additional details.
perl v5.8.0 2003-02-18 H2XS(1)