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.

• /*
   * =============================================================
   * 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.
   * =============================================================
   */
  
  /* $Revision: 1.9 $ */
  
  #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);
  }
  
  /* The gateway routine */
  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