#include <floatingpoint.h>
#include <siginfo.h>

sigfpe_handler_type sigfpe(sigfpe_code_type code,
 sigfpe_handler_type hdl);

The sigfpe() function allows signal handling to be specified for particular SIGFPE codes. A call to sigfpe() defines a new handler hdl for a particular SIGFPE code and returns the old handler as the value of the function sigfpe(). Normally handlers are specified as pointers to functions; the special cases SIGFPE_IGNORE, SIGFPE_ABORT, and SIGFPE_DEFAULT allow ignoring, dumping core using abort(3C), or default handling respectively. Default handling is to dump core using abort(3C).

The code argument is usually one of the five IEEE\|754-related SIGFPE codes:

FPE_FLTRES fp_inexact - floating-point inexact result
FPE_FLTDIV fp_division - floating-point division by zero
FPE_FLTUND fp_underflow - floating-point underflow
FPE_FLTOVF fp_overflow - floating-point overflow
FPE_FLTINV fp_invalid - floating-point invalid operation

And additionally on the x86 architecture:

FPE_FLTDEN fp_denormalized - floating-point denormalized result

Three steps are required to intercept an IEEE\|754-related SIGFPE code with sigfpe():

The sigfpe() function never changes floating-point hardware mode bits affecting IEEE\|754 trapping. No IEEE\|754-related SIGFPE signals will be generated unless those hardware mode bits are enabled.

SIGFPE signals can be handled using sigfpe(), sigaction(2) or signal(3C). In a particular program, to avoid confusion, use only one of these interfaces to handle SIGFPE signals.

Example 1 Example Of A User-Specified Signal Handler

A user-specified signal handler might look like this:

#include <floatingpoint.h>
#include <siginfo.h>
#include <ucontext.h>
/*
* The sample_handler prints out a message then commits suicide.
*/
void
sample_handler(int sig, siginfo_t *sip, ucontext_t *uap) {
 char *label;
 switch (sip->si_code) {
 case FPE_FLTINV: label = "invalid operand"; break;
 case FPE_FLTRES: label = "inexact"; break;
 case FPE_FLTDIV: label = "division-by-zero"; break;
 case FPE_FLTUND: label = "underflow"; break;
 case FPE_FLTOVF: label = "overflow"; break;
 default: label = "???"; break;
 }
 fprintf(stderr,
 "FP exception %s (0x%x) occurred at address %p.\en",
 label, sip->si_code, (void *) sip->si_addr);
 abort();
}

and it might be set up like this:

#include <floatingpoint.h>
#include <siginfo.h>
#include <ucontext.h>
extern void sample_handler(int, siginfo_t *, ucontext_t *);
main(void) {
 sigfpe_handler_type hdl, old_handler1, old_handler2;
/*
 * save current fp_overflow and fp_invalid handlers; set the new
* fp_overflow handler to sample_handler(\|) and set the new
* fp_invalid handler to SIGFPE_ABORT (abort on invalid)
*/
 hdl = (sigfpe_handler_type) sample_handler;
 old_handler1 = sigfpe(FPE_FLTOVF, hdl);
 old_handler2 = sigfpe(FPE_FLTINV, SIGFPE_ABORT);
 .\|.\|.
/*
 * restore old fp_overflow and fp_invalid handlers
 */
 sigfpe(FPE_FLTOVF, old_handler1);
 sigfpe(FPE_FLTINV, old_handler2);
}

See attributes(7) for descriptions of the following attributes:

sigaction (2), abort (3C), signal (3C), floatingpoint.h (3HEAD), attributes (7)

The sigfpe() function returns (void(*)())-1 if code is not zero or a defined SIGFPE code.