How to return the outputs of mexFunction() in Matlab?

Question

I have this code in C:

#include <mex.h>
#include <matrix.h>
#include<stdio.h>
#include <math.h>

//...

 int callFun(int argc, char *argv[]){
     int aa = 4;
     printf ( "\naa value = %d\n",aa);
 return aa;
 }

//...

and I want to call it using Matlab. To do this, I have created this mexFunction()

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
    {
    int argc = 0;
    char **argv;
    int i, result;

    argc = nrhs;
    argv = (char **) mxCalloc( argc, sizeof(char *) );

    for (i = 0; i < nrhs; i++){
        if( !mxIsChar( prhs[i] ) ){
        mexErrMsgTxt("Input must be of type char.");
        return;
        }
        argv[i] = mxArrayToString( prhs[i] );
    }

    result = callFun( argc, argv );

    for( i=argc-1; i>=0; i-- )
        mxFree( argv[i] );

    mxFree( argv );
    if( result )
        mexErrMsgTxt("main function causes an error");
}

However, I do not know how to get aa value, when I call callFun() in Matlab.

>> Outputs = callFun('callFun','ff');  % this should returns aa value

Is it possible to improve mexFunction for better performance?

Answer 1

You can use mxCreateDoubleScalar :

plhs[0] = mxCreateDoubleScalar((double)result);

I suggest you cast the value to double , as that is MATLAB's native type. You can pass the int as int32 to MATLAB, but that is more involved and not as convenient.