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FE_DFL_ENV

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C++
Numerics library
Floating-point environment
Functions
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Macro constants
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FE_DFL_ENV
(C++11)
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.

Example

Run this code 
#include <cfenv>
#include <iostream>
// #pragma STDC FENV_ACCESS ON
void show_env()
{
    const 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";
    switch (std::fegetround())
    {  
        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

See also

(C++11)
saves or restores the current floating-point environment
(function)
(C++11)
restores the floating-point environment and raises the previously raised exceptions
(function)
C documentation for FE_DFL_ENV