function
<cfenv>
feholdexcept
int feholdexcept (fenv_t* envp);
Hold floating-point exceptions
Saves the current state of the floating-point environment in the object pointed by envp. It then resets the current state and -if supported- puts the environment in non-stop mode.
The non-stop mode prevents floating-point exceptions from stopping the normal flow of the program when raised (with traps or abortions).
Programs calling this function shall ensure that pragma FENV_ACCESS is enabled for the call.
Parameters
- envp
- Pointer to a fenv_t object where the state of the floating-point environment is stored.
Return Value
Zero, if the function completed successfully, including setting the floating point environment to non-stop mode.
A non-zero value otherwise.
Example
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/* feholdexcept/feupdateenv example */
#include <stdio.h> /* printf, puts */
#include <fenv.h> /* feholdexcept, feclearexcept, fetestexcept, feupdateenv, FE_* */
#include <math.h> /* log */
#pragma STDC FENV_ACCESS on
double log_zerook (double x) {
fenv_t fe;
feholdexcept(&fe);
x=log(x);
feclearexcept (FE_OVERFLOW|FE_DIVBYZERO);
feupdateenv(&fe);
return x;
}
int main ()
{
feclearexcept (FE_ALL_EXCEPT);
printf ("log(0.0): %f\n", log_zerook(0.0));
if (!fetestexcept(FE_ALL_EXCEPT))
puts ("no exceptions raised");
return 0;
}
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Possible output:
log(0.0): -inf
no exceptions raised
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Data races
Each thread maintains a separate floating-point environment with its own state. Spawning a new thread copies the current state. [This applies to C11 and C++11 implementations]
Exceptions
No-throw guarantee: this function never throws exceptions.
Note that C floating-point exceptions are not C++ exceptions, and thus are not caught by try/catch blocks.
See also
- fegetenv
- Get floating-point environment (function)
- fesetenv
- Set floating-point environment (function)
- feclearexcept
- Clear floating-point exceptions (function)