FE_DFL_ENV

 

C++

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Numerics library

Common mathematical functions
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Mathematical constants (C++20)
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Floating-point environment (C++11)
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gcd (C++17)	lcm (C++17)
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midpoint (C++20)	lerp (C++20)
Saturation arithmetic
add_sat (C++26) sub_sat (C++26) saturate_cast (C++26)	mul_sat (C++26) div_sat (C++26)
Generic numeric operations
iota (C++11) ranges::iota (C++23) accumulate inner_product adjacent_difference partial_sum	reduce (C++17) transform_reduce (C++17) inclusive_scan (C++17) exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
Bit operations
has_single_bit (C++20)     bit_cast (C++20) bit_ceil (C++20) bit_floor (C++20) bit_width (C++20) rotl (C++20) rotr (C++20)	popcount (C++20) countl_zero (C++20) countl_one (C++20) countr_zero (C++20) countr_one (C++20) byteswap (C++23) endian (C++20)

 

Floating-point environment

Functions

feclearexcept (C++11)

fetestexcept (C++11)

feraiseexcept (C++11)

fegetexceptflagfesetexceptflag (C++11)(C++11)

fegetroundfesetround (C++11)(C++11)

fegetenvfesetenv (C++11)(C++11)

feholdexcept (C++11)

feupdateenv (C++11)

Macro constants

FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C++11)(C++11)(C++11)(C++11)(C++11)(C++11)

FE_DOWNWARDFE_TONEARESTFE_TOWARDZEROFE_UPWARD (C++11)(C++11)(C++11)(C++11)

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

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