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

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 valueme

Is it possible to improve mexFunction for better performance?

Answer 1

[James Tursa]

Put this at the bottom of your code. But remember that if you call mexErrMsgTxt your mex function will exit immediately and not return any value, so if you want to see the result you should delete the code that calls mexErrMsgTxt.

plhs[0] = mxCreateDoubleScalar(result);

[shdotcom shdotcom]

Thank you very much. What if I want to return an array of more than one values (with different types), instead of a value?

[James Tursa]

Then you will have to copy the values one-by-one. E.g.,

double *dp, *pr;
int i, n;
// some code here to allocate and assign n values to dp[0], dp[1], etc.
plhs[0] = mxCreateDoubleMatrix(1,n,mxREAL);
pr = mxGetPr(plhs[0]);
for( i=0; i<n; i++ ) {
    pr[i] = dp[i];
}
mxFree(dp);

Or you could use memcpy( ) to copy everything as a block.