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H2XS(1)
NAME
h2xs - convert .h C header files to Perl extensions
SYNOPSIS
h2xs [-ACOPXacdfkmx] [-F addflags] [-M fmask] [-n module_name] [-o tmask]
[-p prefix] [-s subs] [-v version] [headerfile ... [extra_libraries]]
h2xs -h
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 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 HISTORY 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 overwritten.
-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
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.
-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 "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).
-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_wildcard_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 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 the LIMITATIONS of -x entry elsewhere 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 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".
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 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
the perl manpage, the perlxstut manpage, the ExtUtils::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, 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.
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