How to raise a float point exception

Question

guys. I am doing some work around float point operations. The 0.1 is inexact represented by binary float point format. Thus I wrote down this

float i = 0.1f;

and expecting the inexact exception to arise. I turnned on the -fp-trap-all=all option, set fp-mode to be strict and installed SIGFPE signal handler in my code. But nothing happened. Then I tried

float i = 0.1f,j = 0.2f, c;
c = i + j;

still can not catch any exceptions! It drive my crazy.

Sorry to mention that I am using intel c++ compiler on Linux at last.

Answer 1

You have to test for exceptions yourself. The following code works for me:

#include <stdio.h>
#include <fenv.h>

#ifndef FE_INEXACT
#  error No FP Exception handling!
#endif

int main()
{
    double a = 4.0;
    a /= 3.0;

    if (fetestexcept(FE_INEXACT) & FE_INEXACT)
    {
        printf("Exception occurred\n");
    }
    else
    {
        printf("No exception.\n");
    }
}

If you replace 4.0 by 3.0, you will not get the exception.

You can do something similar with double a = 0.0; a = sin(a);.

---

Trapping exceptions are only supported conditionally. To check, use the macros described in the documentation:

#define _GNU_SOURCE
#include <fenv.h>

#ifndef FE_NOMASK_ENV
#  warning Cannot raise FP exceptions!
#else
#  warning Trapping FP exceptions enabled.
feenableexcept(FE_INEXACT);
#endif