Defined in header <cfenv> | ||
|---|---|---|
#define FE_DFL_ENV /*implementation defined*/ | (since C++11) |
The macro constant FE_DFL_ENV expands to an expression of type const std::fenv_t*, which points to a full copy of the default floating-point environment, that is, the environment as loaded at program startup.
Additional macros that begin with FE_ followed by uppercase letters, and have the type const std::fenv_t*, may be supported by an implementation.
#include <iostream>
#include <cfenv>
#pragma STDC FENV_ACCESS ON
void show_env()
{
int e = std::fetestexcept(FE_ALL_EXCEPT);
if(e & FE_DIVBYZERO) std::cout << "division by zero is raised\n";
if(e & FE_INEXACT) std::cout << "inexact is raised\n";
if(e & FE_INVALID) std::cout << "invalid is raised\n";
if(e & FE_UNDERFLOW) std::cout << "underflow is raised\n";
if(e & FE_OVERFLOW) std::cout << "overflow is raised\n";
int r = std::fegetround();
switch(r)
{
case FE_DOWNWARD: std::cout << "rounding down\n"; break;
case FE_TONEAREST: std::cout << "rounding to nearest\n"; break;
case FE_TOWARDZERO: std::cout << "rounding to zero\n"; break;
case FE_UPWARD: std::cout << "rounding up\n"; break;
}
}
int main()
{
std::cout << "On startup: \n";
show_env();
std::feraiseexcept(FE_UNDERFLOW | FE_OVERFLOW);
std::fesetround(FE_UPWARD);
std::cout << "\nBefore restoration: \n";
show_env();
std::fesetenv(FE_DFL_ENV);
std::cout << "\nAfter reset to default: \n";
show_env();
}Output:
On startup: rounding to nearest Before restoration: underflow is raised overflow is raised rounding up After reset to default: rounding to nearest
|
(C++11) | saves or restores the current floating point environment (function) |
|
(C++11) | restores the floating-point environment and raises the previously raise exceptions (function) |
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