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
Normally, only the code between the
- Normal processing code -
- Error processing code -
SPMquotON_ERROR" keywords is executed. If UDI signals an error, however, the code between the
SPMquotENDCATCH" keywords is executed. Note that
SPMquotON_ERROR" is optional; if an error is signaled and it is absent, execution resumes after the
The example program in Figure 2.2 will not run correctly
because the element type of
is not the same as the element type of
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.