Illinois Genetic Algorithms Laboratory

Since many of us use C/C++ to code our GAs, and then use Matlab to plot the results, here’s several simple steps that allow you to call Matlab functions directly from C/C++:

1. Convert the main to mexFunction
mexFunction is the entrance of matlab executable.

mexFunction(int nlhs,mxArray *plhs[],int nrhs,const mxArray *prhs[]) {
    int i;
    int argc  = nrhs;

    char **argv;

    argv = new char * [argc];

    for (i=0; i<argc; i++) {
              int length = mxGetNumberOfElements(prhs[i])+1;
              argv[i] = new char [length];
              mxGetString(prhs[i], argv[i], length);
    }
    ...
}

Basically, prhs are left elements and plhs are right elements.
e.g. In Matlab
[a,b]=xxx(c,d,e);
a and b are prhs, and nrhs = 2
c, d, and e are plhs, and nlhs = 3

2. Convert printf to mexPrintf
This can be done simply by

"#define printf mexPrintf"

3. Error message: mexErrMsgTxt will show text in red (default) in Matlab.

mexErrMsgTxt("blah blah blah");

4. Include “mex.h” everywhere you call mex functions.
mex.h can be found under the maltab directory.

5. To call a matlab function, use mexCallMATLAB
For example, to call a = f(b), where a is a double and b is a 1×2 matrix, the code looks like:

mxArray *plhs, *prhs;
prhs =  mxCreateDoubleMatrix(1, 2, mxREAL);
double *ptr = mxGetPr(prhs);
ptr[0] = b;
ptr[1] = c;
mexCallMATLAB(1, &plhs, 1, &prhs, "f");
a = *mxGetPr(plhs);
mxDestroyArray(plhs);
mxDestroyArray(prhs);

6. Compile the transferred code into mex (in Matlab)

mex -f /usr/local/matlab/bin/cxxopts.sh foo.cpp foo1.cpp foo2.cpp .....

cxxopts.sh are needed to let matlab know that you are doing c/c++.
It can be found under the matlab directory. The 1st name will be used as the library name (foo). In windows, the result is .dll; in Linux, it’s .mexglx.

More mex functions can be found on the MathWorks. Hope that helps.