SwigMatlabPlus

(c) 2001 Sumit Basu, MIT Media Laboratory

Overview

SwigMatlabPlus is a simple extension of SWIG (Simple Wrapper and Interface Generation). This allows you to take C++ code (classes and all) and easily export them to MATLAB. For instance, consider the following class:

class foo {
foo();
~foo();
int x;
int bar(double y);
};

You can access it from matlab with the following:

>> q= foo('new_foo')
q = _1023a_foo_p;
>> foo('foo_bar', 3)
ans=7

I can't take all the credit for this - I borrowed heavily from the MATLAB example in the SWIG source distribution. That version was useful, but could only deal with scalar arguments and did not have C++ class support. I also added support for vectors/matrices through the helper functions described below.

Features

1. Simple interface/code generation for converting C++ modules to MATLAB. No more messing with prhs[0], plhs[0], etc.
2. Class support - access C++ objects, member variables, and methods from MATLAB.
3. Support for vectors and matrices through the fm*Matrix classes (written by Brian Clarkson). Support exists for double, float, int, short, and unsigned char matrices (and it's easy to add others). This is somewhat inefficient in that fmMatrix is row-major (more natural in C) while MATLAB matrices are column major. Furthermore, matrices that live in the MATLAB side need to have their storage allocated by mxCalloc/etc., otherwise bad things happen. However, we're already using fmMatrix classes for a lot of other code, so it was more convenient.To keep this reasonably efficient, I provide helper functions to convert between MATLAB matrices and fmMatrices, so it's up you to decide when to incur the cost of the conversion. Feel free to add your own (hopefully more efficient) matrix classes -- it's not very difficult.
4. Passthrough of the mxArray * class into C++ (see the matlab.map file).

Software

The package swigmatlabplus.zip has a number of components:

1. swigmatlabplus.dsw - the workspace (for Visual C++ 6) to build everything else. You'll have to download the SWIG source to build SwigMatlabPlus, but the rest of the stuff will build as long as you've got MATLAB. You will need to change the settings to correspond to your source/lib directories, of course.
2. swigmatlabplus.exe - the wrapper generation mechanism
3. matfm.dll - helper functions that allow translation from _2353a_fmMatrix_p to a MATLAB matrix and vice versa. These are accessed through the matlab wrapper functions: mat2fm*Matrix.m, mat2fm*Vector.m, fm*Vector2mat.m, and fm*Matrix2mat.m. (The source for this can be found in matfm.dsp)
4. test.h, test.cpp, test.i, test_wrap.cpp, in test.dsp - a simple example that shows how to use this stuff.

Tutorial

An EXTREMELY terse tutorial based on the test* module is coming soon.

Related Information

Building MEX files in Visual Studio (i.e., circumventing the mex script). Note: This is for MATLAB 6 or greater.

Running swigmatlabplus in Visual Studio

Author

Acknowledgements

Thanks to the SWIG team, who did most of the work - this is just an illustration of how easy it is to modify their code for other target languages. Also thanks to Brian Clarkson, who provided the matrix code and had helpful design advice.