HP-UX Floating-Point Guide

Chapter 6 161

Floating-Point Trap Handling

Handling Traps

The ON statement is documented fully in the HP Fortran 90

Programmer’s Reference and the HP FORTRAN/9000 Programmer’s

Guide.

Using the sigaction(2) Function (C only)

For C programs, the standard method of handling errors is to use the

sigaction(2) function. The function establishes the address of a

signal-handling function that is called whenever the speciﬁed HP-UX

signal is raised. The major problem with this method is that there is only

one HP-UX signal, SIGFPE, for all IEEE and integer exceptions. When

SIGFPE is raised, the only way to ﬁnd out which exception generated the

signal is to examine the ﬂoating-point exception registers, which can be

obtained from the sigcontext structure that is an argument to the

sigaction(2) function. (Or you can enable a trap for only one exception.)

The following C program uses fesettrapenable to enable a trap for

the overﬂow exception, and calls sigaction(2) to specify that the function

handle_sigfpe is to be called when SIGFPE is raised.