C(3) User Contributed Perl Documentation C(3)NAME
Inline::C - Write Perl Subroutines in C
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, iff 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";
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.
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;
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. Default is 'ParseRecDescent', which uses
the Parse::RecDescent module. The only other option is 'ParseRegExp',
which uses the Inline::C::ParseRegExp module that ships with Inline.
use Inline C => Config => USING => 'ParseRegExp';
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 occured 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.
1.
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.
2.
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.
3.
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*".
4.
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 occurence 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
1. 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.
AUTHOR
Brian Ingerson <INGY@cpan.org>
Sisyphus <sisyphus@cpan.org> fixed some bugs and is current co-
maintainer.
COPYRIGHT
Copyright (c) 2000-2002. Brian Ingerson.
Copyright (c) 2008, 2010-2012. 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
perl v5.16.2 2012-10-08 C(3)