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Executive Summary

SWIG is an interface compiler that connects programs written in C and C++ with scripting languages such as Perl, Python, Ruby, and Tcl. It works by taking the declarations found in C/C++ header files and using them to generate the wrapper code that scripting languages need to access the underlying C/C++ code. In addition, SWIG provides a variety of customization features that let you tailor the wrapping process to suit your application.

John Ousterhout (creator of Tcl) has written a paper that describes the benefits of scripting languages. SWIG makes it fairly easy to connect scripting languages with C/C++ code.

SWIG is used in a number of ways:

  • Building more powerful C/C++ programs. Using SWIG, you can replace the main() function of a C program with a scripting interpreter from which you can control the application. This adds quite a lot of flexibility and makes the program "programmable." That is, the scripting interface allows users and developers to easily modify the behavior of the program without having to modify low-level C/C++ code. The benefits of this are numerous. In fact think of all of the large software packages that you use every day---nearly all of them include special a macro language, configuration language, or even a scripting engine that allows users to make customizations.

  • Rapid prototyping and debugging. SWIG allows C/C++ programs to be placed in a scripting environment that can be used for testing and debugging. For example, you might test a library with a collection of scripts or use the scripting interpreter as an interactive debugger. Since SWIG requires no modifications to the underlying C/C++ code, it can be used even if the final product does not rely upon scripting.

  • Systems integration. Scripting languages work fairly well for controlling and gluing loosely-coupled software components together. With SWIG, different C/C++ programs can be turned into scripting language extension modules. These modules can then be combined together to create new and interesting applications.

  • Construction of scripting language extension modules. SWIG can be used to turn common C/C++ libraries into components for use in popular scripting languages. Of course, you will still want to make sure that no-one else has already created a module before doing this.

SWIG is sometimes compared to interface definition language (IDL) compilers such as those you find with systems such as CORBA and COM. Although there are a few similarities, the whole point of SWIG is to make it so you don't have to add an extra layer of IDL specifications to your application. If anything, it's much more of a rapid application development and prototyping tool. Specifically:
  • ANSI C/C++ syntax. SWIG parses ANSI C++ that has been extended with a number of special directives. As a result, interfaces are usually built by grabbing a header file and tweaking it a little bit. This particular approach is especially useful when the underlying C/C++ program undergoes frequent modification.

  • SWIG is not a stub generator. SWIG produces code that you simply compile and run. You don't have to fill in any stubs or write special client/server code as you do with RPC-like systems.

  • SWIG does not define a protocol nor is it a component framework. SWIG does not define mechanisms or enforce rules regarding the way in which software components are supposed to interact with each other. Nor is it a specialized runtime library or alternative scripting language API. SWIG is merely a code generator that provides the glue necessary to hook C/C++ to other languages.

  • Designed to work with existing C/C++ code. SWIG requires little, if any, modifications to existing code. For the most part, it encourages you to keep a clean separation between C/C++ and its scripting interface.

  • Extensibility. SWIG provides a variety of customization options that allow you to blow your whole leg off if that's what you want to do. SWIG is not here to enforce programming morality.

Finally, it is worth noting that even though SWIG is occasionally compared to other more specialized scripting language extension building tools (e.g., Perl XS, Python bgen, etc.), its primary audience is C/C++ programmers who want to add a scripting language component to their applications. Because of this, SWIG tends to have a slightly different focus than tools designed to build small modules for widespread use in a scripting language distribution. applications.

A number of papers and tutorials describing SWIG are available. You can also view a simple tutorial to see an example of SWIG in action, or check out how other people are using SWIG in their projects.

SWIG has been freely available in various forms since February, 1996 and a large number of developers have made contributions. Today, SWIG remains an all-volunteer effort. Approximately 875 people subscribe to the swig mailing list and a public Git repository is available at Github. Versions of SWIG can now be found in most Linux distributions (however, you'll almost certainly want to get the latest version here).

Feedback and questions concerning this site should be posted to the swig-devel mailing list.

Last modified : Sat May 13 14:25:49 2017