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
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.
In spite of its name,
h2xs may also be used to create a skeleton pure
Perl module. See the
-X option.
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 a skeleton pure Perl
module. "-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; 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.
- -b, --compat-version=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. 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.
- -e, --omit-enums=[regular
expression]
- If regular expression is not given, skip all
constants that are defined in a C enumeration. Otherwise skip only those
constants that are defined in an enum whose name matches regular
expression.
Since regular expression is optional, make sure that this switch is
followed by at least one other switch if you omit regular
expression and have some pending arguments such as header-file names.
This is ok:
h2xs -e -n Module::Foo foo.h
This is not ok:
h2xs -n Module::Foo -e foo.h
In the latter, foo.h is taken as regular expression.
- -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"-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, --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_wildcard_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 5.6.2.
"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() function 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-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".
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
# Extension is a pure Perl module with no XS code.
h2xs -X My::Module
# Extension is Lib::Foo which works at least with Perl5.005_03.
# Constants are created for all #defines and enums h2xs can find
# in foo.h.
h2xs -b 5.5.3 -n Lib::Foo foo.h
# Extension is Lib::Foo which works at least with Perl5.005_03.
# Constants are created for all #defines but only for enums
# whose names do not start with 'bar_'.
h2xs -b 5.5.3 -e '^bar_' -n Lib::Foo foo.h
# 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 accessible 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 "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¶
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
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 perlxs and perlxstut for additional details.