The _exec, _spawn, and system functions should not be called during the evaluation of a floating-point expression.Resets the floating-point package.
#include <float.h>
void _fpreset( void );
The _fpreset function reinitializes the floating-point-math package. This function is usually used in conjunction with signal, system, or the _exec or _spawn functions.
If a program traps floating-point error signals (SIGFPE) with signal, it can safely recover from floating-point errors by invoking _fpreset and using longjmp.
In DOS versions prior to 3.0, a child process executed by _exec, _spawn, or system may affect the floating-point state of the parent process if an 8087, 80287, or 80387 coprocessor is used. If you are using either coprocessor, the following precautions are recommended:
The _exec, _spawn, and system functions should not be called during the evaluation of a floating-point expression.
The _fpreset function should be called after these routines if there is a possibility of the child process performing any floating-point operations.
None.
Standards:None
16-Bit:DOS, QWIN, WIN, WIN DLL
32-Bit:DOS32X
_exec functions, signal, _spawn functions
/* FPRESET.C: This program uses signal to set up a routine for handling
* floating-point errors.
*/
#include <stdio.h>
#include <signal.h>
#include <setjmp.h>
#include <stdlib.h>
#include <float.h>
#include <math.h>
#include <string.h>
jmp_buf mark; /* Address for long jump to jump to */
int fperr; /* Global error number */
void fphandler( int sig, int num ); /* Prototypes */
void fpcheck( void );
void main( void )
{
double n1, n2, r;
int jmpret;
/* Set up floating-point error handler. The compiler
* will generate a warning because it expects
* signal-handling functions to take only one argument.
*/
if( signal( SIGFPE, fphandler ) == SIG_ERR )
{
fprintf( stderr, "Couldn't set SIGFPE\n" );
abort();
}
/* Save stack environment for return in case of error. First time
* through, jmpret is 0, so true conditional is executed. If an
* error occurs, jmpret will be set to -1 and false conditional
* will be executed.
*/
jmpret = setjmp( mark );
if( jmpret == 0 )
{
printf( "Test for invalid operation - " );
printf( "enter two numbers: " );
scanf( "%lf %lf", &n1, &n2 );
r = n1 / n2;
/* This won't be reached if error occurs. */
printf( "\n\n%4.3g / %4.3g = %4.3g\n", n1, n2, r );
r = n1 * n2;
/* This won't be reached if error occurs. */
printf( "\n\n%4.3g * %4.3g = %4.3g\n", n1, n2, r );
}
else
fpcheck();
}
/* fphandler handles SIGFPE (floating-point error) interrupt. Note
* that this prototype accepts two arguments and that the prototype
* for signal in the run-time library expects a signal handler to
* have only one argument.
*
* The second argument in this signal handler allows processing of
* _FPE_INVALID, _FPE_OVERFLOW, _FPE_UNDERFLOW, and _FPE_ZERODIVIDE
* all of which are Microsoft-specific symbols that augment the
* information provided by SIGFPE. The compiler will generate a
* warning, which is harmless and expected.
*/
void fphandler( int sig, int num )
{
/* Set global for outside check since we don't want
* to do I/O in the handler.
*/
fperr = num;
/* Initialize floating-point package. */
_fpreset();
/* Restore calling environment and jump back to setjmp. Return -1
* so that setjmp will return false for conditional test.
*/
longjmp( mark, -1 );
}
void fpcheck( void )
{
char fpstr[30];
switch( fperr )
{
case _FPE_INVALID:
strcpy( fpstr, "Invalid number" );
break;
case _FPE_OVERFLOW:
strcpy( fpstr, "Overflow" );
break;
case _FPE_UNDERFLOW:
strcpy( fpstr, "Underflow" );
break;
case _FPE_ZERODIVIDE:
strcpy( fpstr, "Divide by zero" );
break;
default:
strcpy( fpstr, "Other floating point error" );
break;
}
printf( "Error %d: %s\n", fperr, fpstr );
}
Test for invalid operation - enter two numbers: 5 0
Error 131: Divide by zero