For other uses, see
Swig
.
The
Simplified Wrapper and Interface Generator
(
SWIG
) is an
open-source software
tool used to connect
computer programs
or
libraries
written in
C
or
C++
with
scripting languages
such as
Lua
,
Perl
,
PHP
,
Python
,
R
,
Ruby
,
Tcl
, and other language implementations like
C#
,
Java
,
JavaScript
,
Go
,
D
,
OCaml
,
Octave
,
Scilab
and
Scheme
. Output can also be in the form of
XML
.
Function
[
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]
The aim is to allow the calling of native functions (that were written in C or C++) by other programming languages, passing complex data types to those functions, keeping memory from being inappropriately freed, inheriting object classes across languages, etc. The programmer writes an interface file containing a list of C/C++ functions to be made visible to an interpreter. SWIG will compile the interface file and generate code in regular C/C++ and the target programming language. SWIG will generate
conversion code
for functions with simple arguments; conversion code for complex types of arguments must be written by the programmer. The SWIG tool creates
source code
that provides the glue between C/C++ and the target language. Depending on the language, this glue comes in two forms:
- a
shared library
that an extant interpreter can link to as some form of extension module, or
- a shared library that can be linked to other programs compiled in the target language (for example, using
Java Native Interface
(JNI) in Java).
- a shared
dynamic library
source code that should be compiled and dynamically loaded (e.g. Node.js native extensions)
SWIG is not used for calling interpreted functions by native code; this must be done by the programmer manually.
Example
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SWIG wraps simple C declarations by creating an interface that closely matches the way in which the declarations would be used in a C program. For example, consider the following interface file:
[3]
%module
example
%inline
%
{
extern
double
sin
(
double
x
);
extern
int
strcmp
(
const
char
*
,
const
char
*
);
extern
int
Foo
;
%
}
#define STATUS 50
#define VERSION "1.1"
In this file, there are two functions
sin()
and
strcmp()
, a global variable
Foo
, and two constants
STATUS
and
VERSION
. When SWIG creates an extension module, these declarations are accessible as scripting language functions, variables, and constants respectively. In Python:
>>>
example
.
sin
(
3
)
0.141120008
>>>
example
.
strcmp
(
'Dave'
,
'Mike'
)
-1
>>>
print
(
example
.
cvar
.
Foo
)
42
>>>
print
(
example
.
STATUS
)
50
>>>
print
(
example
.
VERSION
)
1.1
Purpose
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There are two main reasons to embed a
scripting engine
in an existing C/C++ program:
- The program can then be customized far faster,
via a scripting language instead of C/C++
. The scripting engine may even be exposed to the end-user, so that they can automate common tasks by writing scripts.
- Even if the final product is not to contain the scripting engine, it may nevertheless be very useful for writing test scripts.
There are several reasons to create dynamic libraries that can be loaded into extant interpreters, including:
- Provide access to a C/C++
library
which has no equivalent in the scripting language.
- Write the whole program in the scripting language first, and after
profiling
, rewrite performance-critical code in C or C++.
History
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]
SWIG is written in C and C++ and has been publicly available since February 1996. The initial author and main developer was
David M. Beazley
who developed SWIG while working as a graduate student at
Los Alamos National Laboratory
and the
University of Utah
and while on the faculty at the
University of Chicago
. Development is currently supported by an active group of volunteers led by William Fulton. SWIG has been released under a
GNU General Public License
.
Google Summer of Code
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]
SWIG was a successful participant of
Google Summer of Code
in 2008, 2009, 2012. In 2008, SWIG got four slots. Haoyu Bai spent his summers on SWIG's Python 3.0 Backend, Jan Jezabek worked on Support for generating
COM
wrappers, Cheryl Foil spent her time on Comment 'Translator' for SWIG, and Maciej Drwal worked on a C backend.
In 2009, SWIG again participated in Google Summer of Code. This time four students participated. Baozeng Ding worked on a
Scilab
module. Matevz Jekovec spent time on
C++0x
features. Ashish Sharma spent his summer on an
Objective-C
module, Miklos Vajna spent his time on PHP directors.
In 2012, SWIG participated in Google Summer of Code. This time four out of five students successfully completed the project. Leif Middelschulte worked on a C target language module. Swati Sharma enhanced the Objective-C module. Neha Narang added the new module on JavaScript. Dmitry Kabak worked on source code documentation and
Doxygen
comments.
Alternatives
[
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]
For Python, similar functionality is offered by
SIP
, Pybind11, and
Boost's Boost.python library
.
Projects Using SWIG
[
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]
See also
[
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]
References
[
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]
Further reading
[
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]
External links
[
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]
