H2XS(1) Perl Programmers Reference Guide H2XS(1)NAMEh2xs - convert .h C header files to Perl extensions
SYNOPSISh2xs [-ACOPXacdfkmx] [-F addflags] [-M fmask] [-n mod
ule_name] [-o tmask] [-p prefix] [-s subs] [-v version]
[headerfile ... [extra_libraries]]
h2xs-h
DESCRIPTIONh2xs 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 exten
sion. 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.
OPTIONS-A Omit all autoload facilities. This is the same as -c
but also removes the "use AutoLoader" statement from
the .pm file.
-C Omits creation of the Changes file, and adds a HIS
TORY section to the POD template.
-F addflags
Additional flags to specify to C preprocessor when
scanning header for function declarations. Should
not be used without -x.
-M regular expression
selects functions/macros to process.
-O Allows a pre-existing extension directory to be over
written.
-P Omit the autogenerated stub POD section.
-X Omit the XS portion. Used to generate templates for
a module which is not XS-based. "-c" and "-f" are
implicitly enabled.
-a 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 argu
ments; 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.
-c Omit "constant()" from the .xs file and corresponding
specialised "AUTOLOAD" from the .pm file.
-d Turn on debugging messages.
-f Allows an extension to be created for a header even
if that header is not found in standard include
directories.
-h Print the usage, help and version for this h2xs and
exit.
-k For function arguments declared as "const", omit the
const attribute in the generated XS code.
-m 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 module_name
Specifies a name to be used for the extension, e.g.,
-n RPC::DCE
-o regular expression
Use "opaque" data type for the C types matched by the
regular expression, even if these types are "type
def"-equivalent to types from typemaps. Should not
be used without -x.
This may be useful since, say, types which are "type
def"-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 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 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_wild
card_sid.
-v version
Specify a version number for this extension. This
version number is added to the templates. The
default is 0.01.
-x Automatically generate XSUBs basing on function dec
larations 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 declara
tions 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 else
where in this document.
-b 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.
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 func
tionality, and the corresponding header files. How to
create an extension which makes this functionality access
able 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".
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
make test
Hints
It is important to do "make dist" as early as possi
ble. 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 gener
ated .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
the perl manpage, the perlxstut manpage, the ExtU
tils::MakeMaker manpage, and the AutoLoader manpage.
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 parameter. In particular, argu
ment 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 addi
tional details.
2002-06-25 perl v5.6.1 H2XS(1)
