HP Fortran Programmer's Guide (B3908-90031; September 2011)

Using the ON statement
Chapter 5130
As described in “Handling runtime exceptions” on page 120, the +fp_exception and +FP options provide
control over how a program behaves when a runtime error occurs. The ON statement provides an additional
level of control by enabling your program to handle floating-point and integer exceptions and +Ctrl-C
interrupts. Before an exception can be handled, the flow of control must pass through an ON statement that
specifies:
• The type of the exception
• One of the following actions:
❏ Execute a trap procedure
❏ Ignore the interrupt
❏ Abort the program
The action specified by the ON statement can only be changed by another ON statement that specifies the
same exception.
This chapter describes how to use the ON statement. The syntax of the ON statement is described in the
HP Fortran Programmer’s Reference. For detailed information about trapping math errors, see the HP-UX
Floating-Point Guide.
NOTE If you include the ON statement in a program that you optimize at level 2 or higher and the
program takes an exception, the results may vary from those you would get from an
unoptimized program or from a program that didn’t have the ON statement.