NAME
Inline::C - C Language Support for Inline
VERSION
This document describes Inline::C version 0.76.
DESCRIPTION
Inline::C is a module that allows you to write Perl subroutines in C.
Since version 0.30 the Inline module supports multiple programming
languages and each language has its own support module. This document
describes how to use Inline with the C programming language. It also
goes a bit into Perl C internals.
If you want to start working with programming examples right away,
check out Inline::C::Cookbook. For more information on Inline in
general, see Inline.
USAGE
You never actually use Inline::C directly. It is just a support module
for using Inline.pm with C. So the usage is always:
use Inline C => ...;
or
bind Inline C => ...;
FUNCTION DEFINITIONS
The Inline grammar for C recognizes certain function definitions (or
signatures) in your C code. If a signature is recognized by Inline,
then it will be available in Perl-space. That is, Inline will generate
the "glue" necessary to call that function as if it were a Perl
subroutine. If the signature is not recognized, Inline will simply
ignore it, with no complaints. It will not be available from
Perl-space, although it will be available from C-space.
Inline looks for ANSI/prototype style function definitions. They must
be of the form:
return-type function-name ( type-name-pairs ) { ... }
The most common types are: int, long, double, char*, and SV*. But you
can use any type for which Inline can find a typemap. Inline uses the
typemap file distributed with Perl as the default. You can specify more
typemaps with the typemaps configuration option.
A return type of void may also be used. The following are examples of
valid function definitions.
int Foo(double num, char* str) {
void Foo(double num, char* str) {
void Foo(SV*, ...) {
long Foo(int i, int j, ...) {
SV* Foo(void) { # 'void' arg invalid with the ParseRecDescent parser.
# Works only with the ParseRegExp parser.
# See the section on `using` (below).
SV* Foo() { # Alternative to specifying 'void' arg. Is valid with
# both the ParseRecDescent and ParseRegExp parsers.
The following definitions would not be recognized:
Foo(int i) { # no return type
int Foo(float f) { # no (default) typemap for float
int Foo(num, str) double num; char* str; {
Notice that Inline only looks for function definitions, not function
prototypes. Definitions are the syntax directly preceding a function
body. Also Inline does not scan external files, like headers. Only the
code passed to Inline is used to create bindings; although other
libraries can linked in, and called from C-space.
C CONFIGURATION OPTIONS
For information on how to specify Inline configuration options, see
Inline. This section describes each of the configuration options
available for C. Most of the options correspond either to MakeMaker or
XS options of the same name. See ExtUtils::MakeMaker and perlxs.
auto_include
Specifies extra statements to automatically included. They will be
added onto the defaults. A newline char will be automatically added.
use Inline C => config => auto_include => '#include "yourheader.h"';
autowrap
If you enable => autowrap, Inline::C will parse function declarations
(prototype statements) in your C code. For each declaration it can
bind to, it will create a dummy wrapper that will call the real
function which may be in an external library. This is a nice
convenience for functions that would otherwise just require an empty
wrapper function.
This is similar to the base functionality you get from h2xs. It can
be very useful for binding to external libraries.
boot
Specifies C code to be executed in the XS BOOT section. Corresponds
to the XS parameter.
cc
Specify which compiler to use.
ccflags
Specify compiler flags - same as ExtUtils::MakeMaker's CCFLAGS
option. Whatever gets specified here replaces the default
$Config{ccflags}. Often, you'll want to add an extra flag or two
without clobbering the default flags in which case you could instead
use ccflagsex (see below) or, if Config.pm has already been loaded:
use Inline C => Config => ccflags => $Config{ccflags} . " -DXTRA -DTOO";
ccflagsex
Extend compiler flags. Sets CCFLAGS to $Config{ccflags} followed by a
space, followed by the specified value:
use Inline C => config => ccflagsex => "-DXTRA -DTOO";
cppflags
Specify preprocessor flags. Passed to cpp C preprocessor by
Preprocess() in Inline::Filters.
use Inline C => <<'END',
CPPFLAGS => ' -DPREPROCESSOR_DEFINE',
FILTERS => 'Preprocess';
use Inline C => <<'END',
CPPFLAGS => ' -DPREPROCESSOR_DEFINE=4321',
FILTERS => 'Preprocess';
filters
Allows you to specify a list of source code filters. If more than one
is requested, be sure to group them with an array ref. The filters
can either be subroutine references or names of filters provided by
the supplementary Inline::Filters module.
Your source code will be filtered just before it is parsed by Inline.
The MD5 fingerprint is generated before filtering. Source code
filters can be used to do things like stripping out POD
documentation, pre-expanding #include statements or whatever else you
please. For example:
use Inline C => DATA =>
filters => [Strip_POD => \&MyFilter => Preprocess ];
Filters are invoked in the order specified. See Inline::Filters for
more information.
If a filter is an array reference, it is assumed to be a usage of a
filter plug- in named by the first element of that array reference.
The rest of the elements of the array reference are used as arguments
to the filter. For example, consider a filters parameter like this:
use Inline C => DATA => filters => [ [ Ragel => '-G2' ] ];
In order for Inline::C to process this filter, it will attempt to
require the module Inline::Filters::Ragel and will then call the
filter function in that package with the argument '-G2'. This
function will return the actual filtering function.
inc
Specifies an include path to use. Corresponds to the MakeMaker
parameter. Expects a fully qualified path.
use Inline C => config => inc => '-I/inc/path';
ld
Specify which linker to use.
lddlflags
Specify which linker flags to use.
NOTE: These flags will completely override the existing flags,
instead of just adding to them. So if you need to use those too, you
must respecify them here.
libs
Specifies external libraries that should be linked into your code.
Corresponds to the MakeMaker parameter. Provide a fully qualified
path with the -L switch if the library is in a location where it
won't be found automatically.
use Inline C => config => libs => '-lyourlib';
or
use Inline C => config => libs => '-L/your/path -lyourlib';
make
Specify the name of the 'make' utility to use.
myextlib
Specifies a user compiled object that should be linked in.
Corresponds to the MakeMaker parameter. Expects a fully qualified
path.
use Inline C => config => myextlib => '/your/path/yourmodule.so';
optimize
This controls the MakeMaker OPTIMIZE setting. By setting this value
to '-g', you can turn on debugging support for your Inline
extensions. This will allow you to be able to set breakpoints in your
C code using a debugger like gdb.
prefix
Specifies a prefix that will be automatically stripped from C
functions when they are bound to Perl. Useful for creating wrappers
for shared library API-s, and binding to the original names in Perl.
Also useful when names conflict with Perl internals. Corresponds to
the XS parameter.
use Inline C => config => prefix => 'ZLIB_';
pre_head
Specifies code that will precede the inclusion of all files specified
in auto_include (ie EXTERN.h, perl.h, XSUB.h, INLINE.h and anything
else that might have been added to auto_include by the user). If the
specified value identifies a file, the contents of that file will be
inserted, otherwise the specified value is inserted.
use Inline C => config => pre_head => $code_or_filename;
prototype
Corresponds to the XS keyword 'PROTOTYPE'. See the perlxs
documentation for both 'PROTOTYPES' and 'PROTOTYPE'. As an example,
the following will set the PROTOTYPE of the 'foo' function to '$',
and disable prototyping for the 'bar' function.
use Inline C => config => prototype => {foo => '$', bar => 'DISABLE'}
prototypes
Corresponds to the XS keyword 'PROTOTYPES'. Can take only values of
'ENABLE' or 'DISABLE'. (Contrary to XS, default value is 'DISABLE').
See the perlxs documentation for both 'PROTOTYPES' and 'PROTOTYPE'.
use Inline C => config => prototypes => 'ENABLE';
typemaps
Specifies extra typemap files to use. These types will modify the
behaviour of the C parsing. Corresponds to the MakeMaker parameter.
Specify either a fully qualified path or a path relative to the cwd
(ie relative to what the cwd is at the time the script is loaded).
use Inline C => config => typemaps => '/your/path/typemap';
using
Specifies which parser to use. The default is
Inline::C::Parser::RecDescent, which uses the Parse::RecDescent
module.
The other options are ::Parser::Pegex and ::Parser::RegExp, which
uses the Inline::C::Parser::Pegex and Inline::C::Parser::RegExp
modules that ship with Inline::C.
use Inline C => config => using => '::Parser::Pegex';
Note that the following old options are deprecated, but still work at
this time:
* ParseRecDescent
* ParseRegExp
* ParsePegex
C-PERL BINDINGS
This section describes how the Perl variables get mapped to C variables
and back again.
First, you need to know how Perl passes arguments back and forth to
subroutines. Basically it uses a stack (also known as the Stack). When
a sub is called, all of the parenthesized arguments get expanded into a
list of scalars and pushed onto the Stack. The subroutine then pops all
of its parameters off of the Stack. When the sub is done, it pushes all
of its return values back onto the Stack.
The Stack is an array of scalars known internally as SV's. The Stack is
actually an array of pointers to SV or SV*; therefore every element of
the Stack is natively a SV*. For FMTYEWTK about this, read perldoc
perlguts.
So back to variable mapping. XS uses a thing known as "typemaps" to
turn each SV* into a C type and back again. This is done through
various XS macro calls, casts and the Perl API. See perldoc perlapi. XS
allows you to define your own typemaps as well for fancier non-standard
types such as typedef- ed structs.
Inline uses the default Perl typemap file for its default types. This
file is called /usr/local/lib/perl5/5.6.1/ExtUtils/typemap, or
something similar, depending on your Perl installation. It has
definitions for over 40 types, which are automatically used by Inline.
(You should probably browse this file at least once, just to get an
idea of the possibilities.)
Inline parses your code for these types and generates the XS code to
map them. The most commonly used types are:
* int
* long
* double
* char*
* void
* SV*
If you need to deal with a type that is not in the defaults, just use
the generic SV* type in the function definition. Then inside your code,
do the mapping yourself. Alternatively, you can create your own typemap
files and specify them using the typemaps configuration option.
A return type of void has a special meaning to Inline. It means that
you plan to push the values back onto the Stack yourself. This is what
you need to do to return a list of values. If you really don't want to
return anything (the traditional meaning of void) then simply don't
push anything back.
If ellipsis or ... is used at the end of an argument list, it means
that any number of SV*s may follow. Again you will need to pop the
values off of the Stack yourself.
See "Examples" below.
THE INLINE STACK MACROS
When you write Inline C, the following lines are automatically
prepended to your code (by default):
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "INLINE.h"
The file INLINE.h defines a set of macros that are useful for handling
the Perl Stack from your C functions.
Inline_Stack_Vars
You'll need to use this one, if you want to use the others. It sets
up a few local variables: sp, items, ax and mark, for use by the
other macros. It's not important to know what they do, but I mention
them to avoid possible name conflicts.
NOTE: Since this macro declares variables, you'll need to put it with
your other variable declarations at the top of your function. It must
come before any executable statements and before any other
Inline_Stack macros.
Inline_Stack_Items
Returns the number of arguments passed in on the Stack.
Inline_Stack_Item(i)
Refers to a particular SV* in the Stack, where i is an index number
starting from zero. Can be used to get or set the value.
Inline_Stack_Reset
Use this before pushing anything back onto the Stack. It resets the
internal Stack pointer to the beginning of the Stack.
Inline_Stack_Push(sv)
Push a return value back onto the Stack. The value must be of type
SV*.
Inline_Stack_Done
After you have pushed all of your return values, you must call this
macro.
Inline_Stack_Return(n)
Return n items on the Stack.
Inline_Stack_Void
A special macro to indicate that you really don't want to return
anything. Same as:
Inline_Stack_Return(0);
Please note that this macro actually returns from your function.
Each of these macros is available in 3 different styles to suit your
coding tastes. The following macros are equivalent.
Inline_Stack_Vars
inline_stack_vars
INLINE_STACK_VARS
All of this functionality is available through XS macro calls as well.
So why duplicate the functionality? There are a few reasons why I
decided to offer this set of macros. First, as a convenient way to
access the Stack. Second, for consistent, self documenting, non-cryptic
coding. Third, for future compatibility. It occurred to me that if a
lot of people started using XS macros for their C code, the interface
might break under Perl6. By using this set, hopefully I will be able to
insure future compatibility of argument handling.
Of course, if you use the rest of the Perl API, your code will most
likely break under Perl6. So this is not a 100% guarantee. But since
argument handling is the most common interface you're likely to use, it
seemed like a wise thing to do.
WRITING C SUBROUTINES
The definitions of your C functions will fall into one of the following
four categories. For each category there are special considerations.
int Foo(int arg1, char* arg2, SV* arg3) {
This is the simplest case. You have a non void return type and a
fixed length argument list. You don't need to worry about much. All
the conversions will happen automatically.
void Foo(int arg1, char* arg2, SV* arg3) {
In this category you have a void return type. This means that either
you want to return nothing, or that you want to return a list. In the
latter case you'll need to push values onto the Stack yourself. There
are a few Inline macros that make this easy. Code something like
this:
int i, max; SV* my_sv[10];
Inline_Stack_Vars;
Inline_Stack_Reset;
for (i = 0; i < max; i++)
Inline_Stack_Push(my_sv[i]);
Inline_Stack_Done;
After resetting the Stack pointer, this code pushes a series of
return values. At the end it uses Inline_Stack_Done to mark the end
of the return stack.
If you really want to return nothing, then don't use the
Inline_Stack_ macros. If you must use them, then set use
Inline_Stack_Void at the end of your function.
char* Foo(SV* arg1, ...) {
In this category you have an unfixed number of arguments. This means
that you'll have to pop values off the Stack yourself. Do it like
this:
int i;
Inline_Stack_Vars;
for (i = 0; i < Inline_Stack_Items; i++)
handle_sv(Inline_Stack_Item(i));
The return type of Inline_Stack_Item(i) is SV*.
void* Foo(SV* arg1, ...) {
In this category you have both a void return type and an unfixed
number of arguments. Just combine the techniques from Categories 3
and 4.
EXAMPLES
Here are a few examples. Each one is a complete program that you can
try running yourself. For many more examples see Inline::C::Cookbook.
Example #1 - Greetings
This example will take one string argument (a name) and print a
greeting. The function is called with a string and with a number. In
the second case the number is forced to a string.
Notice that you do not need to #include <stdio.h>. The perl.h header
file which gets included by default, automatically loads the standard C
header files for you.
use Inline C;
greet('Ingy');
greet(42);
__END__
__C__
void greet(char* name) {
printf("Hello %s!\n", name);
}
Example #2 - and Salutations
This is similar to the last example except that the name is passed in
as a SV* (pointer to Scalar Value) rather than a string (char*). That
means we need to convert the SV to a string ourselves. This is
accomplished using the SvPVX function which is part of the Perl
internal API. See perldoc perlapi for more info.
One problem is that SvPVX doesn't automatically convert strings to
numbers, so we get a little surprise when we try to greet 42. The
program segfaults, a common occurrence when delving into the guts of
Perl.
use Inline C;
greet('Ingy');
greet(42);
__END__
__C__
void greet(SV* sv_name) {
printf("Hello %s!\n", SvPVX(sv_name));
}
Example #3 - Fixing the problem
We can fix the problem in Example #2 by using the SvPV function
instead. This function will stringify the SV if it does not contain a
string. SvPV returns the length of the string as it's second parameter.
Since we don't care about the length, we can just put PL_na there,
which is a special variable designed for that purpose.
use Inline C;
greet('Ingy');
greet(42);
__END__
__C__
void greet(SV* sv_name) {
printf("Hello %s!\n", SvPV(sv_name, PL_na));
}
SEE ALSO
For general information about Inline see Inline.
For sample programs using Inline with C see Inline::C::Cookbook.
For information on supported languages and platforms see
Inline-Support.
For information on writing your own Inline Language Support Module, see
Inline-API.
Inline's mailing list is inline@perl.org
To subscribe, send email to inline-subscribe@perl.org
BUGS AND DEFICIENCIES
If you use C function names that happen to be used internally by Perl,
you will get a load error at run time. There is currently no
functionality to prevent this or to warn you. For now, a list of Perl's
internal symbols is packaged in the Inline module distribution under
the filename 'symbols.perl'. Avoid using these in your code.
AUTHORS
Ingy döt Net <ingy@cpan.org>
Sisyphus <sisyphus@cpan.org>
COPYRIGHT AND LICENSE
Copyright 2000-2015. Ingy döt Net.
Copyright 2008, 2010-2014. Sisyphus.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
See http://www.perl.com/perl/misc/Artistic.html