Preface

# 1 Preface

- Introduction
- SWIG Versions
- SWIG License
- SWIG resources
- Prerequisites
- Organization of this manual
- How to avoid reading the manual
- Backwards compatibility
- Release notes
- Credits
- Bug reports
- Installation
  - Windows installation
  - Unix installation
  - Macintosh OS X installation
  - Testing
  - Examples

## 1.1 Introduction

SWIG (Simplified Wrapper and Interface Generator) is a software development tool for building scripting language interfaces to C and C++ programs. Originally developed in 1995, SWIG was first used by scientists in the Theoretical Physics Division at Los Alamos National Laboratory for building user interfaces to simulation codes running on the Connection Machine 5 supercomputer. In this environment, scientists needed to work with huge amounts of simulation data, complex hardware, and a constantly changing code base. The use of a scripting language interface provided a simple yet highly flexible foundation for solving these types of problems. SWIG simplifies development by largely automating the task of scripting language integration--allowing developers and users to focus on more important problems.

Although SWIG was originally developed for scientific applications, it has since evolved into a general purpose tool that is used in a wide variety of applications--in fact almost anything where C/C++ programming is involved.

## 1.2 SWIG Versions

In the late 1990's, the most stable version of SWIG was release 1.1p5. Versions 1.3.x were officially development versions and these were released over a period of 10 years starting from the year 2000. The final version in the 1.3.x series was 1.3.40, but in truth the 1.3.x series had been stable for many years. An official stable version was released along with the decision to make SWIG license changes and this gave rise to version 2.0.0 in 2010. Version 3.0.0 was released in 2014 focusing on adding C++11 support and C++ nested classes. Version 4.0.0 was released in 2019 to add in Doxygen support. Some target languages were disabled as part of a clean up and others were given a new status of either 'Supported' or 'Experimental'.

## 1.3 SWIG License

The LICENSE file shipped with SWIG in the top level directory contains the SWIG license. For further insight into the license including the license of SWIG's output code, please visit the SWIG legal page - https://www.swig.org/legal.html.

The license was clarified in version 2.0.0 so that the code that SWIG generated could be distributed under license terms of the user's choice/requirements and at the same time the SWIG source was placed under the GNU General Public License version 3.

## 1.4 SWIG resources

The official location of SWIG related material is

    https://www.swig.org

This site contains the latest version of the software, users guide, and information regarding bugs, installation problems, and implementation tricks.

You can also subscribe to the swig-user mailing list by visiting the page

    https://www.swig.org/mail.html

The mailing list often discusses some of the more technical aspects of SWIG along with information about beta releases and future work.

Git and Subversion access to the latest version of SWIG is also available. More information about this can be obtained at:

    SWIG Bleeding Edge

## 1.5 Prerequisites

This manual assumes that you know how to write C/C++ programs and that you have at least heard of scripting languages such as Tcl, Python, and Perl. A detailed knowledge of these scripting languages is not required although some familiarity won't hurt. No prior experience with building C extensions to these languages is required---after all, this is what SWIG does automatically. However, you should be reasonably familiar with the use of compilers, linkers, and makefiles since making scripting language extensions is somewhat more complicated than writing a normal C program.

Over time SWIG releases have become significantly more capable in their C++ handling--especially support for advanced features like namespaces, overloaded operators, and templates. Whenever possible, this manual tries to cover the technicalities of this interface. However, this isn't meant to be a tutorial on C++ programming. For many of the gory details, you will almost certainly want to consult a good C++ reference. If you don't program in C++, you may just want to skip those parts of the manual.

## 1.6 Organization of this manual

The first few chapters of this manual describe SWIG in general and provide an overview of its capabilities. The remaining chapters are devoted to specific SWIG language modules and are self contained. Thus, if you are using SWIG to build Python interfaces, you can probably skip to that chapter and find almost everything you need to know.

## 1.7 How to avoid reading the manual

If you hate reading manuals, glance at the "Introduction" which contains a few simple examples. These examples contain about 95% of everything you need to know to use SWIG. After that, simply use the language-specific chapters as a reference. The SWIG distribution also comes with a large directory of examples that illustrate different topics.

## 1.8 Backwards compatibility

If you are a previous user of SWIG, don't expect SWIG to provide complete backwards compatibility. Although the developers strive to the utmost to keep backwards compatibility, this isn't always possible as the primary goal over time is to make SWIG better---a process that would simply be impossible if the developers are constantly bogged down with backwards compatibility issues. Potential incompatibilities are clearly marked in the detailed release notes.

If you need to work with different versions of SWIG and backwards compatibility is an issue, you can use the SWIG_VERSION preprocessor symbol which holds the version of SWIG being executed. SWIG_VERSION is a hexadecimal integer such as 0x010311 (corresponding to SWIG-1.3.11). This can be used in an interface file to define different typemaps, take advantage of different features etc:

    #if SWIG_VERSION >= 0x010311
    /* Use some fancy new feature */
    #endif

Note: The version symbol is not defined in the generated SWIG wrapper file. The SWIG preprocessor has defined SWIG_VERSION since SWIG-1.3.11.

## 1.9 Release notes

The CHANGES.current, CHANGES and RELEASENOTES files shipped with SWIG in the top level directory contain, respectively, detailed release notes for the current version, detailed release notes for previous releases and summary release notes from SWIG-1.3.22 onwards.

## 1.10 Credits

SWIG is an unfunded project that would not be possible without the contributions of many people working in their spare time. If you have benefitted from using SWIG, please consider Donating to SWIG to keep development going. There have been a large varied number of people who have made contributions at all levels over time. Contributors are mentioned either in the COPYRIGHT file or CHANGES files shipped with SWIG or in submitted bugs.

## 1.11 Bug reports

Although every attempt has been made to make SWIG bug-free, we are also trying to make feature improvements that may introduce bugs. To report a bug, either send mail to the SWIG developer list at the swig-devel mailing list or report a bug at the SWIG bug tracker. In your report, be as specific as possible, including (if applicable), error messages, tracebacks (if a core dump occurred), corresponding portions of the SWIG interface file used, and any important pieces of the SWIG generated wrapper code. We can only fix bugs if we know about them.

## 1.12 Installation

### 1.12.1 Windows installation

Please see the dedicated Windows chapter for instructions on installing SWIG on Windows and running the examples. The Windows distribution is called swigwin and includes a prebuilt SWIG executable, swig.exe, included in the top level directory. Otherwise it is exactly the same as the main SWIG distribution. There is no need to download anything else.

### 1.12.2 Unix installation

These installation instructions are for using the distributed tarball, for example, `swig-3.0.8.tar.gz`. If you wish to build and install from source on Github, extra steps are required. Please see the Bleeding Edge page on the SWIG website.

You must use GNU make to build and install SWIG.

PCRE2 needs to be installed on your system to build SWIG, in particular pcre2-config must be available. If you have PCRE2 headers and libraries but not pcre2-config itself or, alternatively, wish to override the compiler or linker flags returned by pcre2-config, you may set PCRE2_LIBS and PCRE2_CFLAGS variables to be used instead. And if you don't have PCRE2 at all, the configure script will provide instructions for obtaining it.

To build and install SWIG, simply type the following:

    $ ./configure
    $ make
    $ make install

By default SWIG installs itself in /usr/local. If you need to install SWIG in a different location or in your home directory, use the `--prefix` option to `./configure`. For example:

    $ ./configure --prefix=/home/yourname/projects
    $ make
    $ make install

Note: the directory given to `--prefix` must be an absolute pathname. Do not use the ~ shell-escape to refer to your home directory. SWIG won't work properly if you do this.

The INSTALL file shipped in the top level directory details more about using configure. Also try

    $ ./configure --help.

The configure script will attempt to locate various packages on your machine including Tcl, Perl5, Python and all the other target languages that SWIG supports. Don't panic if you get 'not found' messages -- SWIG does not need these packages to compile or run. The configure script is actually looking for these packages so that you can try out the SWIG examples contained in the 'Examples' directory without having to hack Makefiles. Note that the `--without-xxx` options, where xxx is a target language, have minimal effect. All they do is reduce the amount of testing done with 'make check'. The SWIG executable and library files installed cannot currently be configured with a subset of target languages.

SWIG used to include a set of runtime libraries for some languages for working with multiple modules. These are no longer built during the installation stage. However, users can build them just like any wrapper module as described in the Modules chapter. The CHANGES file shipped with SWIG in the top level directory also lists some examples which build the runtime library.

Note:

- If you checked the code out via Git, you will have to run `./autogen.sh` before `./configure`. In addition, a full build of SWIG requires a number of packages to be installed. Full instructions at SWIG bleeding edge.

### 1.12.3 Macintosh OS X installation

SWIG is known to work on various flavors of OS X. Follow the Unix installation instructions above. However, as of this writing, there is still great deal of inconsistency with how shared libraries are handled by various scripting languages on OS X.

Users of OS X should be aware that Darwin handles shared libraries and linking in a radically different way than most Unix systems. In order to test SWIG and run the examples, SWIG configures itself to use flat namespaces and to allow undefined symbols (`-flat_namespace -undefined suppress`). This mostly closely follows the Unix model and makes it more likely that the SWIG examples will work with whatever installation of software you might have. However, this is generally not the recommended technique for building larger extension modules. Instead, you should utilize Darwin's two-level namespaces. Some details about this can be found here Understanding Two-Level Namespaces.

Needless to say, you might have to experiment a bit to get things working at first.

### 1.12.4 Testing

If you want to test SWIG after building it, a check can be performed on Unix operating systems. Type the following:

        $ make -k check

This step can be performed either before or after installation. The check requires at least one of the target languages to be installed. If it fails, it may mean that you have an uninstalled language module or that the file 'Examples/Makefile' has been incorrectly configured. It may also fail due to compiler issues such as a broken C++ compiler. Even if the check fails, there is a pretty good chance SWIG still works correctly --- you will just have to mess around with one of the examples and some makefiles to get it to work. Some tests may also fail due to missing dependency packages, eg PCRE or Boost, but this will require careful analysis of the configure output done during configuration.

The test suite executed by the check is designed to stress-test many parts of the implementation including obscure corner cases. If some of these tests fail or generate warning messages, there is no reason for alarm --- the test may be related to some new SWIG feature or a difficult bug that we're trying to resolve. Chances are that SWIG will work just fine for you. Note that if you have more than one CPU/core, then you can use parallel make to speed up the check as it does take quite some time to run, for example:

        $ make -j2 -k check

Also, SWIG's support for C++ is sufficiently advanced that certain tests may fail on older C++ compilers (for instance if your compiler does not support member templates). These errors are harmless if you don't intend to use these features in your own programs.

Note: The test-suite currently contains over 600 tests. If you have many different target languages installed and a slow machine, it might take more than an hour to run the test-suite.

### 1.12.5 Examples

The Examples directory contains a variety of examples of using SWIG and it has some browsable documentation. Simply point your browser to the file "Example/index.html".

The Examples directory also includes Visual C++ project 6 (.dsp) files for building some of the examples on Windows. Later versions of Visual Studio will convert these old style project files into a current solution file.