Using the C Math Library

Customizing Error Handling 

Two aspects of the default error handling behavior of the MATLAB C Math Library routines may not suit every application:

• Exiting on error conditions
• Displaying error messages to the same display as other application messages.

You may want control to return to your application when an error occurs, allowing it to perform clean up processing before exiting. You may also prefer to direct error and warning messages to a different output stream than the normal messages output by your application. The following sections describe how to make these customizations.

Continuing Processing After Errors

To return control to your application after a library routine encounters an error condition, you must define try and catch blocks in your application.

When you define a try block, the library warning-level processing does not change. The routines output a warning message and return control back to the application. The default library error processing, however, does change. When you define a try block, the library routines do not output an error message to the user and then exit. Instead, the routines transfer control to your catch block, which performs the error handling processing.

For example, if you want to output an error message to the user, you must do so from your catch block. (You can use the mlfLasterr() routine to obtain the text of the message associated with the most recent error that occurred.)

Defining a Try Block.   A try block is a group of one or more statements, enclosed in braces, introduced by the mlfTry macro:

mlfTry
{
    /* your code */
}

Note that the mlfTry macro does not require parentheses; it is not a procedure call.

Defining a Catch Block.   A catch block is a group of one or more routines, enclosed in braces, introduced by the mlfCatch macro and terminated by the mlfEndCatch macro:

mlfCatch
{
    /* Your code */
}
mlfEndCatch

The catch block contains error processing code. For example, you could put clean-up code in your catch block to free allocated storage before exiting. The mlfCatch and mlfEndCatch macros do not require parentheses.

Note    While this error handling mechanism is modeled on the C++ exception handling facility, there is no connection between the two. The MATLAB C Math Library does not "throw" exceptions, as the MATLAB C++ Math Library does. The syntax used with the macros is different than the C++ keywords. The library error handling mechanism is built on the setjmp/longjmp mechanism. For more information about setjmp/longjmp, see your system documentation.

Error Handling Overview

Example - Defining Try/Catch Blocks (ex6.c)