Using the C Math Library

Error Handling Overview 

The MATLAB C Math library routines handle error conditions in two ways, depending on the severity of the error:

• For less-severe error conditions, the library routines output a warning message to the user and then return control to the application. The application can continue processing.
• For more-severe error conditions, the library routines output a message to the user and then exit, terminating the application. Control never returns to the application.

The following example program illustrates this default library error handling. The program deliberately causes a warning-level error condition, division by zero, and a more severe error condition, attempting to add two matrices of unequal size, that causes termination.

#include <stdio.h>
#include <stdlib.h>     /* used for EXIT_SUCCESS */
#include <string.h>
#include "matlab.h" 

/* Matrix data. Column-major element order */
static double data[] = { 1, 2, 3, 4, 5, 6 };

main()
{
    /* Declare matrix variables */
    mxArray *mat0 = NULL;
    mxArray *mat1 = NULL;
    mxArray *mat2 = NULL;

    mlfEnterNewContext(0,0);
    
    /* Create two matrices of different sizes */
    mlfAssign(&mat0, mlfDoubleMatrix(2, 3, data, NULL));
    mlfAssign(&mat1, mlfDoubleMatrix(3, 2, data, NULL));

    /* Division by zero will produce a warning */
    mlfAssign(&mat2, mlfRdivide(mat1, mlfScalar(0)));
    mlfPrintf("Return to application after warning.\n");

    /* Adding mismatched matrices produces error */
    mlfPrintMatrix(mlfPlus(mat0, mat1));
    mlfPrintf("Should not be reached after error.\n");

    /* Free any matrices that were assigned to variables */
    mxDestroyArray(mat2);
    mxDestroyArray(mat0);
    mxDestroyArray(mat1);
    
    mlfRestorePreviousContext(0, 0);
    return(EXIT_SUCCESS);
}

This program produces the following output. You can see how this program continues processing after a warning, but terminates after an error.

WARNING: Divide by zero.
Return to application after warning.
ERROR: Matrix dimensions must agree.

EXITING

Handling Errors and Writing a Print Handler

Customizing Error Handling