std::fegetround, std::fesetround - cppreference.com (original) (raw)

Manages the floating-point rounding direction.

1. Attempts to establish the floating-point rounding direction equal to the argument round, which is expected to be one of the floating point rounding macros.

[edit] Parameters

[edit] Return value

1. ​0​ on success, non-zero otherwise.

2. The floating point rounding macro describing the current rounding direction or a negative value if the direction cannot be determined.

[edit] Notes

The current rounding mode, reflecting the effects of the most recent fesetround, can also be queried with FLT_ROUNDS.

See floating-point rounding macros for the effects of rounding.

[edit] Example

#include #include #include #include #include // #pragma STDC FENV_ACCESS ON   int main() { static constexpr std::pair<const char*, const double> samples[] { {" 12.0", 12.0}, {" 12.1", 12.1}, {"-12.1", -12.1}, {" 12.5", 12.5}, {"-12.5", -12.5}, {" 12.9", 12.9}, {"-12.9", -12.9}, {" 13.0", 13.0} };   std::cout << "│ sample │ FE_DOWNWARD │ FE_UPWARD │ FE_TONEAREST │ FE_TOWARDZERO │\n";   for (const auto& [str, fp] : samples) { std::cout << "│ " << std::setw(6) << str << " │ "; for (const int dir : {FE_DOWNWARD, FE_UPWARD, FE_TONEAREST, FE_TOWARDZERO}) { std::fesetround(dir); std::cout << std::setw(10) << std::fixed << std::nearbyint(fp) << " │ "; } std::cout << '\n'; } }

Output:

│ sample │ FE_DOWNWARD │ FE_UPWARD │ FE_TONEAREST │ FE_TOWARDZERO │ │ 12.0 │ 12.000000 │ 12.000000 │ 12.000000 │ 12.000000 │ │ 12.1 │ 12.000000 │ 13.000000 │ 12.000000 │ 12.000000 │ │ -12.1 │ -13.000000 │ -12.000000 │ -12.000000 │ -12.000000 │ │ 12.5 │ 12.000000 │ 13.000000 │ 12.000000 │ 12.000000 │ │ -12.5 │ -13.000000 │ -12.000000 │ -12.000000 │ -12.000000 │ │ 12.9 │ 12.000000 │ 13.000000 │ 13.000000 │ 12.000000 │ │ -12.9 │ -13.000000 │ -12.000000 │ -13.000000 │ -12.000000 │ │ 13.0 │ 13.000000 │ 13.000000 │ 13.000000 │ 13.000000 │

[edit] See also