std::rint, std::rintf, std::rintl, std::lrint, std::lrintf, std::lrintl, std::llrint, std::llrintf (original) (raw)
| Defined in header | ||
|---|---|---|
| Rounding to floating-point types | ||
| (1) | ||
| float rint ( float num ); double rint ( double num ); long double rint ( long double num ); | (since C++11) (until C++23) | |
| /* floating-point-type */ rint( /* floating-point-type */ num ); | (since C++23) | |
| float rintf( float num ); | (2) | (since C++11) |
| long double rintl( long double num ); | (3) | (since C++11) |
| Rounding to long | ||
| (4) | ||
| long lrint ( float num ); long lrint ( double num ); long lrint ( long double num ); | (since C++11) (until C++23) | |
| long lrint ( /* floating-point-type */ num ); | (since C++23) | |
| long lrintf( float num ); | (5) | (since C++11) |
| long lrintl( long double num ); | (6) | (since C++11) |
| Rounding to long long | ||
| (7) | ||
| long long llrint ( float num ); long long llrint ( double num ); long long llrint ( long double num ); | (since C++11) (until C++23) | |
| long long llrint ( /* floating-point-type */ num ); | (since C++23) | |
| long long llrintf( float num ); | (8) | (since C++11) |
| long long llrintl( long double num ); | (9) | (since C++11) |
| Additional overloads | ||
| Defined in header | ||
| template< class Integer > double rint( Integer num ); | (A) | (since C++11) |
| template< class Integer > long lrint( Integer num ); | (B) | (since C++11) |
| template< class Integer > long long llrint( Integer num ); | (C) | (since C++11) |
1-3) Rounds the floating-point argument num to an integer value (in floating-point format), using the current rounding mode. The library provides overloads of std::rint for all cv-unqualified floating-point types as the type of the parameter num.(since C++23)
4-9) Rounds the floating-point argument num to an integer value, using the current rounding mode. The library provides overloads of std::lrint and std::llrint for all cv-unqualified floating-point types as the type of the parameter num.(since C++23)
A-C) Additional overloads are provided for all integer types, which are treated as double.
[edit] Parameters
| num | - | floating-point or integer value |
|---|
[edit] Return value
If no errors occur, the nearest integer value to num, according to the current rounding mode, is returned.
[edit] Error handling
Errors are reported as specified in math_errhandling.
If the result of std::lrint or std::llrint is outside the range representable by the return type, a domain error or a range error may occur.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
For the std::rint function:
- If num is ±∞, it is returned, unmodified.
- If num is ±0, it is returned, unmodified.
- If num is NaN, NaN is returned.
For std::lrint and std::llrint functions:
- If num is ±∞, FE_INVALID is raised and an implementation-defined value is returned.
- If the result of the rounding is outside the range of the return type, FE_INVALID is raised and an implementation-defined value is returned.
- If num is NaN, FE_INVALID is raised and an implementation-defined value is returned.
[edit] Notes
POSIX specifies that all cases where std::lrint or std::llrint raise FE_INEXACT are domain errors.
As specified in math_errhandling, FE_INEXACT may be (but isn't required to be on non-IEEE floating-point platforms) raised by std::rint when rounding a non-integer finite value.
The only difference between std::rint and std::nearbyint is that std::nearbyint never raises FE_INEXACT.
The largest representable floating-point values are exact integers in all standard floating-point formats, so std::rint never overflows on its own; however the result may overflow any integer type (including std::intmax_t), when stored in an integer variable.
If the current rounding mode is:
- FE_DOWNWARD, then
std::rintis equivalent to std::floor. - FE_UPWARD, then
std::rintis equivalent to std::ceil. - FE_TOWARDZERO, then
std::rintis equivalent to std::trunc. - FE_TONEAREST, then
std::rintdiffers from std::round in that halfway cases are rounded to even rather than away from zero.
The additional overloads are not required to be provided exactly as (A-C). They only need to be sufficient to ensure that for their argument num of integer type:
- std::rint(num) has the same effect as std::rint(static_cast<double>(num)).
- std::lrint(num) has the same effect as std::lrint(static_cast<double>(num)).
- std::llrint(num) has the same effect as std::llrint(static_cast<double>(num)).
[edit] Example
#include #include #include #include // #pragma STDC FENV_ACCESS ON int main() { std::fesetround(FE_TONEAREST); std::cout << "Rounding to nearest (halfway cases to even):\n" << " rint(+2.3) = " << std::rint(2.3) << '\n' << " rint(+2.5) = " << std::rint(2.5) << '\n' << " rint(+3.5) = " << std::rint(3.5) << '\n' << " rint(-2.3) = " << std::rint(-2.3) << '\n' << " rint(-2.5) = " << std::rint(-2.5) << '\n' << " rint(-3.5) = " << std::rint(-3.5) << '\n'; std::fesetround(FE_DOWNWARD); std::cout << "Rounding down:\n" << " rint(+2.3) = " << std::rint(2.3) << '\n' << " rint(+2.5) = " << std::rint(2.5) << '\n' << " rint(+3.5) = " << std::rint(3.5) << '\n' << " rint(-2.3) = " << std::rint(-2.3) << '\n' << " rint(-2.5) = " << std::rint(-2.5) << '\n' << " rint(-3.5) = " << std::rint(-3.5) << '\n' << "Rounding down with lrint:\n" << " lrint(+2.3) = " << std::lrint(2.3) << '\n' << " lrint(+2.5) = " << std::lrint(2.5) << '\n' << " lrint(+3.5) = " << std::lrint(3.5) << '\n' << " lrint(-2.3) = " << std::lrint(-2.3) << '\n' << " lrint(-2.5) = " << std::lrint(-2.5) << '\n' << " lrint(-3.5) = " << std::lrint(-3.5) << '\n' << "Special values:\n" << " lrint(-0.0) = " << std::lrint(-0.0) << '\n' << std::hex << std::showbase << " lrint(-Inf) = " << std::lrint(-INFINITY) << '\n'; // error handling std::feclearexcept(FE_ALL_EXCEPT); std::cout << "std::rint(0.1) = " << std::rint(.1) << '\n'; if (std::fetestexcept(FE_INEXACT)) std::cout << " FE_INEXACT was raised\n"; std::feclearexcept(FE_ALL_EXCEPT); std::cout << "std::lrint(LONG_MIN-2048.0) = " << std::lrint(LONG_MIN - 2048.0) << '\n'; if (std::fetestexcept(FE_INVALID)) std::cout << " FE_INVALID was raised\n"; }
Possible output:
Rounding to nearest (halfway cases to even): rint(+2.3) = 2 rint(+2.5) = 2 rint(+3.5) = 4 rint(-2.3) = -2 rint(-2.5) = -2 rint(-3.5) = -4 Rounding down: rint(+2.3) = 2 rint(+2.5) = 2 rint(+3.5) = 4 rint(-2.3) = -2 rint(-2.5) = -2 rint(-3.5) = -4 Rounding down with lrint: lrint(+2.3) = 2 lrint(+2.5) = 2 lrint(+3.5) = 3 lrint(-2.3) = -3 lrint(-2.5) = -3 lrint(-3.5) = -4 Special values: lrint(-0.0) = 0 lrint(-Inf) = 0x8000000000000000 std::rint(0.1) = 0 std::lrint(LONG_MIN-2048.0) = 0x8000000000000000 FE_INVALID was raised