H2XS(1) Perl Programmers Reference Guide H2XS(1) #
H2XS(1) Perl Programmers Reference Guide H2XS(1)
NNAAMMEE #
h2xs - convert .h C header files to Perl extensions
SSYYNNOOPPSSIISS #
hh22xxss [OOPPTTIIOONNSS ...] [headerfile ... [extra_libraries]]
hh22xxss --hh|--??|----hheellpp
DDEESSCCRRIIPPTTIIOONN #
_h_2_x_s 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 _m_o_d_u_l_e___n_a_m_e 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 --LL//aannootthheerr//lliibbrraarryy//ppaatthh in the extra-
libraries argument.
In spite of its name, _h_2_x_s may also be used to create a skeleton pure
Perl module. See the --XX option.
OOPPTTIIOONNSS #
--AA, ----oommiitt--aauuttoollooaadd
Omit all autoload facilities. This is the same as --cc but also
removes the "use AutoLoader" statement from the .pm file.
--BB, ----bbeettaa--vveerrssiioonn
Use an alpha/beta style version number. Causes version number to be
"0.00_01" unless --vv is specified.
--CC, ----oommiitt--cchhaannggeess
Omits creation of the _C_h_a_n_g_e_s file, and adds a HISTORY section to
the POD template.
--FF, ----ccpppp--ffllaaggss=_a_d_d_f_l_a_g_s
Additional flags to specify to C preprocessor when scanning header
for function declarations. Writes these options in the generated
_M_a_k_e_f_i_l_e_._P_L too.
--MM, ----ffuunncc--mmaasskk=_r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n
selects functions/macros to process.
--OO, ----oovveerrwwrriittee--ookk
Allows a pre-existing extension directory to be overwritten.
--PP, ----oommiitt--ppoodd
Omit the autogenerated stub POD section.
--XX, ----oommiitt--XXSS
Omit the XS portion. Used to generate a skeleton pure Perl module.
"-c" and "-f" are implicitly enabled.
--aa, ----ggeenn--aacccceessssoorrss
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.
--bb, ----ccoommppaatt--vveerrssiioonn=_v_e_r_s_i_o_n
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.
--cc, ----oommiitt--ccoonnssttaanntt
Omit "constant()" from the .xs file and corresponding specialised
"AUTOLOAD" from the .pm file.
--dd, ----ddeebbuuggggiinngg
Turn on debugging messages.
--ee, ----oommiitt--eennuummss=[_r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n]
If _r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n 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 _r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n.
Since _r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n is optional, make sure that this switch is
followed by at least one other switch if you omit _r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n
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 _r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n.
--ff, ----ffoorrccee
Allows an extension to be created for a header even if that header
is not found in standard include directories.
--gg, ----gglloobbaall
Include code for safely storing static data in the .xs file.
Extensions that do no make use of static data can ignore this
option.
--hh, --??, ----hheellpp
Print the usage, help and version for this h2xs and exit.
--kk, ----oommiitt--ccoonnsstt--ffuunncc
For function arguments declared as "const", omit the const attribute
in the generated XS code.
--mm, ----ggeenn--ttiieedd--vvaarr
EExxppeerriimmeennttaall: for each variable declared in the header file(s),
declare a perl variable of the same name magically tied to the C
variable.
--nn, ----nnaammee=_m_o_d_u_l_e___n_a_m_e
Specifies a name to be used for the extension, e.g., -n RPC::DCE
--oo, ----ooppaaqquuee--rree=_r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n
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 --xx.
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).
--pp, ----rreemmoovvee--pprreeffiixx=_p_r_e_f_i_x
Specify a prefix which should be removed from the Perl function
names, e.g., -p sec_rgy_ This sets up the XS PPRREEFFIIXX keyword and
removes the prefix from functions that are autoloaded via the
"constant()" mechanism.
--ss, ----ccoonnsstt--ssuubbss=_s_u_b_1_,_s_u_b_2
Create a perl subroutine for the specified macros rather than
autoload with the ccoonnssttaanntt(()) subroutine. These macros are assumed
to have a return type of cchhaarr **, e.g.,
-s sec_rgy_wildcard_name,sec_rgy_wildcard_sid.
--tt, ----ddeeffaauulltt--ttyyppee=_t_y_p_e
Specify the internal type that the ccoonnssttaanntt(()) 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.
----uussee--nneeww--tteessttss
When ----ccoommppaatt--vveerrssiioonn (--bb) 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".
----uussee--oolldd--tteessttss
Will force the generation of test code that uses the older "Test"
module.
----sskkiipp--eexxppoorrtteerr
Do not use "Exporter" and/or export any symbol.
----sskkiipp--ppppppoorrtt
Do not use "Devel::PPPort": no portability to older version.
----sskkiipp--aauuttoollooaaddeerr
Do not use the module "AutoLoader"; but keep the ccoonnssttaanntt(()) function
and "sub AUTOLOAD" for constants.
----sskkiipp--ssttrriicctt
Do not use the pragma "strict".
----sskkiipp--wwaarrnniinnggss
Do not use the pragma "warnings".
--vv, ----vveerrssiioonn=_v_e_r_s_i_o_n
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.
--xx, ----aauuttooggeenn--xxssuubbss
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 --xx".
EEXXAAMMPPLLEESS #
# 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
EExxtteennssiioonn bbaasseedd oonn _._h aanndd _._c ffiilleess 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 _i_n_t_e_r_f_a_c_e___s_i_m_p_l_e_._h and _i_n_t_e_r_f_a_c_e___h_a_i_r_y_._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 _E_x_t_/_E_n_s_i_o_n.
Copy C files
Copy your header files and C files to this directory _E_x_t_/_E_n_s_i_o_n.
Create the extension
Run h2xs, overwriting older autogenerated files:
h2xs -Oxan Ext::Ension interface_simple.h interface_hairy.h
h2xs looks for header files _a_f_t_e_r 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 mmeerrggee(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 _._p_m 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.
EENNVVIIRROONNMMEENNTT #
No environment variables are used.
AAUUTTHHOORR #
Larry Wall and others
SSEEEE AALLSSOO #
perl, perlxstut, ExtUtils::MakeMaker, and AutoLoader.
DDIIAAGGNNOOSSTTIICCSS #
The usual warnings if it cannot read or write the files involved.
LLIIMMIITTAATTIIOONNSS ooff --xx _h_2_x_s 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, _h_2_x_s 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.
perl v5.36.3 2024-03-20 H2XS(1)