HP-UX Floating-Point Guide

164 Chapter 6

Floating-Point Trap Handling

Detecting Exceptions without Enabling Traps

Detecting Exceptions without Enabling

Traps

If you do not enable traps for ﬂoating-point exceptions, you can still

determine whether the exceptions have occurred. When an exception

occurs and the corresponding exception trap enable bit is not set, the

system sets the corresponding exception ﬂag. The exception ﬂags are

cumulative; once a ﬂag is set, it remains set for the duration of the

program unless you clear it. (This is why the exception ﬂags are also

called sticky bits.)

At critical points in your program, you can call the fetestexcept

function (described in “Manipulating the Exception Flags:

fegetexceptﬂag, fesetexceptﬂag, fetestexcept, feraiseexcept,

feclearexcept” on page 133) to determine whether an exception has

occurred. You can then respond to the exception as you wish. The

program example in that section illustrates the use of this function.

NOTE Be careful if you use these functions at higher optimization levels (2 and

above). See “Run-Time Mode Control: The fenv(5) Suite” on page 127.