fetestexcept fails

[rembremading]

Hi all!

I try to implement floating point error handling, (i.e. trap nan and if
errors in floating point opperations) with gnu c standard library.
However fetestexcept does not give me the expected result.
The following code prints
Floating point error:
without the expected error code

Thank you!

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <fenv.h>
#include <setjmp.h>
#include <signal.h>
#include <math.h>
 
 
#ifndef __SUPPORT_SNAN__
#define __SUPPORT_SNAN__
#endif
 
jmp_buf return_to_top_level;
 
 
/* floating-point error handler */
void fperror(int sig)
{
 
int ret;
int set_excepts;
char temp[256];
 
strcpy(temp, "Floating point error: ");
 
set_excepts = fetestexcept(FE_INEXACT | FE_DIVBYZERO | FE_UNDERFLOW |
FE_OVERFLOW);
 
if(set_excepts & FE_INEXACT)
strcat(temp,"[Inexact] ");
 
if(set_excepts & FE_DIVBYZERO)
strcat(temp,"[Divide by 0] ");
 
if(set_excepts & FE_UNDERFLOW)
strcat(temp,"[Underflow] ");
 
if(set_excepts & FE_OVERFLOW)
strcat(temp,"[Overflow] ");
 
if(set_excepts & FE_INVALID)
strcat(temp,"[Invalid] ");
 
printf("\a%s\n", temp);
 
keep_going = 0;
longjmp(return_to_top_level, 1);
 
}
 
int main()
{
 
double test1, test2;
int ret;
 
/* assigning exception handler */
 
signal(SIGFPE, fperror);
 
/* enableing floating point exception signaling */
ret = feenableexcept(FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW);
 
/* set-up return address for errors */
if(setjmp(return_to_top_level)){
return 1;
}
 
test1 = 0.0;
test2 = 3.14/test1;
test1 = -1.0;
test2 = sqrt(test1);
 
return EXIT_SUCCESS;
}

[jacob navia]

rembremading wrote:

Hi all!

[snip]

You have several errors in your code. I rewrote it
like this, and compiled it with lcc-win32. It should
also compile with gcc since it is pure C99

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <fenv.h>
#include <setjmp.h>
#include <signal.h>
#include <math.h>
 
 
#ifndef __SUPPORT_SNAN__
#define __SUPPORT_SNAN__
#endif
 
jmp_buf return_to_top_level;
 
 
/* floating-point error handler */
void fperror(int sig)
{
 
int ret;
int set_excepts;
char temp[256];
 
strcpy(temp, "Floating point error: ");
 
set_excepts = fetestexcept(FE_INEXACT | FE_DIVBYZERO | FE_UNDERFLOW |
FE_OVERFLOW);
 
if(set_excepts & FE_INEXACT)
strcat(temp,"[Inexact] ");
 
if(set_excepts & FE_DIVBYZERO)
strcat(temp,"[Divide by 0] ");
 
if(set_excepts & FE_UNDERFLOW)
strcat(temp,"[Underflow] ");
 
if(set_excepts & FE_OVERFLOW)
strcat(temp,"[Overflow] ");
 
if(set_excepts & FE_INVALID)
strcat(temp,"[Invalid] ");
 
printf("\a%s\n", temp);
 
// NOT DEFINED keep_going = 0;
longjmp(return_to_top_level, 1);
 
}
 
int main()
{
 
double test1, test2;
int ret;
fenv_t env;
fexcept_t flagp;
 
/* assigning exception handler */
 
signal(SIGFPE, fperror);
 
fegetexceptflag(&flagp,FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW);
/* enableing floating point exception signaling */
fesetexceptflag(&flagp,FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW);
 
/* set-up return address for errors */
if(setjmp(return_to_top_level)){
return 1;
}
 
test1 = 0.0;
test2 = 3.14/test1;
fperror(0);
test1 = -1.0;
test2 = sqrt(test1);
fperror(0);
 
return EXIT_SUCCESS;
}

[rembremading]

Yes it works!
I conclude, that the main error (appart from improper copy&paste) was, that
I forgot to define
fenv_t env;
fexcept_t flagp;
and to hand over &flagp to fegetexceptflag.
My gcc compiler did not complain. (but I dont wont to blame it)

Thank you.


jacob navia wrote:

rembremading wrote:

>Hi all!

[snip]

You have several errors in your code. I rewrote it
like this, and compiled it with lcc-win32. It should
also compile with gcc since it is pure C99

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <fenv.h>
#include <setjmp.h>
#include <signal.h>
#include <math.h>
 
 
#ifndef __SUPPORT_SNAN__
         #define __SUPPORT_SNAN__
#endif
 
jmp_buf return_to_top_level;
 
 
/* floating-point error handler */
void fperror(int sig)
{
 
int ret;
int set_excepts;
char temp[256];
 
strcpy(temp, "Floating point error: ");
 
set_excepts = fetestexcept(FE_INEXACT | FE_DIVBYZERO | FE_UNDERFLOW |
FE_OVERFLOW);
 
if(set_excepts & FE_INEXACT)
         strcat(temp,"[Inexact] ");
 
if(set_excepts & FE_DIVBYZERO)
         strcat(temp,"[Divide by 0] ");
 
if(set_excepts & FE_UNDERFLOW)
         strcat(temp,"[Underflow] ");
 
if(set_excepts & FE_OVERFLOW)
         strcat(temp,"[Overflow] ");
 
if(set_excepts & FE_INVALID)
         strcat(temp,"[Invalid] ");
 
         printf("\a%s\n", temp);
 
         // NOT DEFINED keep_going = 0;
         longjmp(return_to_top_level, 1);
 
}
 
int main()
{
 
double test1, test2;
int ret;
fenv_t env;
fexcept_t flagp;
 
/* assigning exception handler */
 
   signal(SIGFPE, fperror);
 
   fegetexceptflag(&flagp,FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW);
/* enableing floating point exception signaling */
   fesetexceptflag(&flagp,FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW);
 
/* set-up return address for errors */
if(setjmp(return_to_top_level)){
         return 1;
}
 
test1 = 0.0;
test2 = 3.14/test1;
fperror(0);
test1 = -1.0;
test2 = sqrt(test1);
fperror(0);
 
return EXIT_SUCCESS;
}