2.5 Error handling

UDI has a very robust error detection/reporting mechanism. For many common programming errors, the UDI messages are so detailed that the user does not need to resort to a source code debugger.

When UDI detects an error, one or more messages are printed and an error is signaled. The error signal can be caught in the user's program with the ERRORCATCH", ON_ERROR", and ENDCATCH" macros.

SPMquotERRORCATCH"

		 - Normal processing code - 
SPMquotON_ERROR" 
		 - Error processing code - 
ENDCATCH" 

Normally, only the code between the SPMquotERRORCATCH" and SPMquotON_ERROR" keywords is executed. If UDI signals an error, however, the code between the SPMquotON_ERROR" and SPMquotENDCATCH" keywords is executed. Note that SPMquotON_ERROR" is optional; if an error is signaled and it is absent, execution resumes after the SPMquotENDCATCH".

 

Figure 2.2: An example of using ERRORCATCH

The example program in Figure 2.2 will not run correctly because the element type  of result" is not the same as the element type of vector1" and SPMquotvector2". When the program is run, we get the following output:

% example
vmul: the data type of 'result' must be equal to real.
OOPS! Detected an error
%

If the user has not used the SPMquotERRORCATCH" mechanism and UDI signals an error, the abort()" routine is called which causes a core dump (on Unix systems) to aid in debugging. The user can specify a different routine by calling error_handler(fptr)" where fptr is a pointer to a function returning an integer (int (*fptr)()"). Note that the error handling routine should eventually call exit()" since it is not possible to recover from most UDI errors.