| Common mathematical functions | |||||||||||||||||||||||||||||||
| Mathematical special functions(C++17) | |||||||||||||||||||||||||||||||
| Mathematical constants(C++20) | |||||||||||||||||||||||||||||||
| Basic linear algebra algorithms(C++26) | |||||||||||||||||||||||||||||||
| Data-parallel types (SIMD)(C++26) | |||||||||||||||||||||||||||||||
| Floating-point environment(C++11) | |||||||||||||||||||||||||||||||
| Complex numbers | |||||||||||||||||||||||||||||||
Numeric array (valarray) | |||||||||||||||||||||||||||||||
| Pseudo-random number generation | |||||||||||||||||||||||||||||||
| Bit manipulation(C++20) | |||||||||||||||||||||||||||||||
| Saturation arithmetic(C++26) | |||||||||||||||||||||||||||||||
| Factor operations | |||||||||||||||||||||||||||||||
|
| ||||||||||||||||||||||||||||||
| Interpolations | |||||||||||||||||||||||||||||||
|
| ||||||||||||||||||||||||||||||
| Generic numeric operations | |||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||
| C-style checked integer arithmetic | |||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||
| Functions | ||||
(C++11) | ||||
(C++11) | ||||
(C++11) | ||||
(C++11)(C++11) | ||||
(C++11)(C++11) | ||||
(C++11)(C++11) | ||||
(C++11) | ||||
(C++11) | ||||
| Macro constants | ||||
(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) | ||||
(C++11) |
Defined in header <cfenv> | ||
#define FE_DOWNWARD /*implementation defined*/ | (since C++11) | |
#define FE_TONEAREST /*implementation defined*/ | (since C++11) | |
#define FE_TOWARDZERO /*implementation defined*/ | (since C++11) | |
#define FE_UPWARD /*implementation defined*/ | (since C++11) | |
Each of these macro constants expands to a nonnegative integer constant expression, which can be used withstd::fesetround andstd::fegetround to indicate one of the supported floating-point rounding modes. The implementation may define additional rounding mode constants in<cfenv>, which should all begin withFE_ followed by at least one uppercase letter. Each macro is only defined if it is supported.
| Constant | Explanation |
FE_DOWNWARD | rounding towards negative infinity |
FE_TONEAREST | rounding towards nearest representable value |
FE_TOWARDZERO | rounding towards zero |
FE_UPWARD | rounding towards positive infinity |
Additional rounding modes may be supported by an implementation.
The current rounding mode affects the following:
double x=1;x/10;// 0.09999999999999999167332731531132594682276248931884765625// or 0.1000000000000000055511151231257827021181583404541015625
std::sqrt(2);// 1.41421356237309492343001693370752036571502685546875// or 1.4142135623730951454746218587388284504413604736328125
double d=1+std::numeric_limits<double>::epsilon();float f= d;// 1.00000000000000000000000// or 1.00000011920928955078125
std::stof("0.1");// 0.0999999940395355224609375// or 0.100000001490116119384765625
std::lrint(2.1);// 2 or 3
The current rounding mode does NOT affect the following:
As with anyfloating-point environment functionality, rounding is only guaranteed if#pragma STDC FENV_ACCESS ON is set.
Compilers that do not support the pragma may offer their own ways to support current rounding mode. For example Clang and GCC have the option-frounding-math intended to disable optimizations that would change the meaning of rounding-sensitive code.
#include <cfenv>#include <cmath>#include <iomanip>#include <iostream>#include <string>// #pragma STDC FENV_ACCESS ON int main(){std::fesetround(FE_DOWNWARD);std::cout<<"rounding down:\n"<<std::setprecision(50)<<" pi = "<<std::acos(-1.f)<<'\n'<<"stof(\"1.1\") = "<<std::stof("1.1")<<'\n'<<" rint(2.1) = "<<std::rint(2.1)<<"\n\n";std::fesetround(FE_UPWARD);std::cout<<"rounding up:\n"<<" pi = "<<std::acos(-1.f)<<'\n'<<"stof(\"1.1\") = "<<std::stof("1.1")<<'\n'<<" rint(2.1) = "<<std::rint(2.1)<<'\n';}
Output:
rounding down: pi = 3.141592502593994140625stof("1.1") = 1.099999904632568359375 rint(2.1) = 2 rounding up: pi = 3.1415927410125732421875stof("1.1") = 1.10000002384185791015625 rint(2.1) = 3| indicates floating-point rounding modes (enum)[edit] | |
(C++11)(C++11) | gets or sets rounding direction (function)[edit] |
C documentation forfloating-point rounding macros | |
