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h2xs - convert .h C header files to Perl extensions
h2xs [-ACOPXacdfkmx] [-F addflags] [-M fmask] [-n module_name] [-o tmask] [-p prefix] [-s subs] [-v version] [headerfile ... [extra_libraries]]
h2xs -h
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.
use AutoLoader
statement from the .pm file.
Changes
file, and adds a HISTORY section to
the POD template.
-c
and -f
are implicitly enabled.
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.
constant()
from the .xs file and corresponding specialised
AUTOLOAD
from the .pm file.
const
, omit the const attribute in the
generated XS code.
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 types.
The type-to-match is whitewashed (except for commas, which have no
whitespace before them, and multiple *
which have no whitespace
between them).
constant()
mechanism.
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 the LIMITATIONS of -x entry elsewhere in this document.
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.
# 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
.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 preprocessor directives and/or
linking with external libraries, see the flags -F
, -L
and -l
in the section on OPTIONS elsewhere in this document.
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
.
Ext/Ension
.
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.
cd Ext/Ension perl Makefile.PL make dist make make test
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
the perl manpage, the perlxstut manpage, the ExtUtils::MakeMaker manpage, and the AutoLoader manpage.
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 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 the perlxs manpage and the perlxstut manpage for additional details.