External Interfaces/API

Calling Functions from C MEX-Files

It is possible to call MATLAB functions, operators, M-files, and other MEX-files from within your C source code by using the API function mexCallMATLAB. This example creates an mxArray, passes various pointers to a subfunction to acquire data, and calls mexCallMATLAB to calculate the sine function and plot the results.

/* $ Revision: 1.4 $ */
/*=============================================================
 * sincall.c
 *
 * Example for illustrating how to use mexCallMATLAB
 * 
 * Creates an mxArray and passes its associated pointers (in
 * this demo, only pointer to its real part, pointer to number of
 * rows, pointer to number of columns) to subfunction fill() to
 * get data filled up, then calls mexCallMATLAB to calculate sin
 * function and plot the result.
 *
 * This is a MEX-file for MATLAB.
 * Copyright (c) 1984-2000 The MathWorks, Inc.
 *============================================================*/
#include "mex.h"
#define MAX 1000

/* Subroutine for filling up data */
void fill( double *pr, int *pm, int *pn, int max )
{
    int i;  
    /* You can fill up to max elements, so (*pr)<=max. */
    *pm = max/2;
    *pn = 1;
    for (i=0; i < (*pm); i++) 
      pr[i]=i*(4*3.14159/max);
}

/* Gateway function */
void mexFunction( int nlhs, mxArray *plhs[],
                  int nrhs, const mxArray *prhs[] )
{
    int     m, n, max=MAX;
    mxArray *rhs[1], *lhs[1];

    rhs[0] = mxCreateDoubleMatrix(max, 1, mxREAL);

    /* Pass the pointers and let fill() fill up data. */
    fill(mxGetPr(rhs[0]), &m, &n, MAX);
    mxSetM(rhs[0], m);
    mxSetN(rhs[0], n);
    

    /* Get the sin wave and plot it. */
    mexCallMATLAB(1, lhs, 1, rhs, "sin");
    mexCallMATLAB(0, NULL, 1, lhs, "plot");

    /* Clean up allocated memory. */
    mxDestroyArray(rhs[0]);
    mxDestroyArray(lhs[0]);
     
    return;
}

Running this example

sincall

displays the results

Note    It is possible to generate an object of type mxUNKNOWN_CLASS using mexCallMATLAB. See the example below.

The following example creates an M-file that returns two variables but only assigns one of them a value.

    function [a,b]=foo[c]
    a=2*c;

MATLAB displays the following warning message.

    Warning: One or more output arguments not assigned during call
    to 'foo'.

If you then call foo using mexCallMATLAB, the unassigned output variable will now be of type mxUNKNOWN_CLASS.

Handling Sparse Arrays

Advanced Topics