std::rint
STD：Rint，STD：：lrint，std：：llrint
| Defined in header | | |
|---|---|---|
| float rint( float arg | (1) | (since C++11) |
| double rint( double arg | (2) | (since C++11) |
| long double rint( long double arg | (3) | (since C++11) |
| double rint( Integral arg | (4) | (since C++11) |
| long lrint( float arg | (5) | (since C++11) |
| long lrint( double arg | (6) | (since C++11) |
| long lrint( long double arg | (7) | (since C++11) |
| long lrint( Integral arg | (8) | (since C++11) |
| long long llrint( float arg | (9) | (since C++11) |
| long long llrint( double arg | (10) | (since C++11) |
| long long llrint( long double arg | (11) | (since C++11) |
| long long llrint( Integral arg | (12) | (since C++11) |
1-3%29圈浮点参数arg为浮点格式%29的整数值%28，使用电流舍入模式...
5-7，9-11%29圈浮点参数arg值的整数值，则使用电流舍入模式...
4，8，12%29一组过载或接受任意参数的函数模板积分型。等于%282，6，10%29，分别为%28double29%。
参数
| arg | - | floating point value |
|---|
返回值
如果没有发生错误，则最近的整数值为arg，根据电流舍入模式，被归还。
错误处理
错误按数学[医]错误处理...
如果...的结果...std::lrint或std::llrint在返回类型可表示的范围之外，可能会发生域错误或范围错误。
如果实现支持ieee浮点算术%28iec 60559%29，则对std::rint职能：
- 如果
arg是±∞，它被返回，未经修改
- 如果
arg是±0，它被返回，未经修改
- 如果
arg是南，南回来了
为std::lrint和std::llrint职能：
- 如果
arg是±∞，FE_INVALID引发，并返回实现定义的值。
- 如果舍入的结果超出了返回类型的范围，
FE_INVALID引发，并返回实现定义的值。
- 如果
arg是南FE_INVALID引发，并返回实现定义的值。
注记
POSIX指定所有案件std::lrint或std::llrint提高FE_INEXACT是域错误。
如数学[医]错误处理，，，FE_INEXACT可能为%28，但%27T是否需要在非ieee浮点平台上由std::rint当舍入一个非整数的有限值时。
唯一的区别是std::rint和std::nearbyint那是std::nearbyint不养FE_INEXACT...
最大的可表示浮点值是所有标准浮点格式的精确整数，因此std::rint永远不要自己溢出，但是结果可能会溢出任何整数类型%28，包括std::intmax_t%29，存储在整数变量中。
如果当前舍入模式是..。
FE_DOWNWARD，然后std::rint等于std::floor...
FE_UPWARD，然后std::rint等于std::ceil...
FE_TOWARDZERO，然后std::rint等于std::trunc
FE_TONEAREST，然后std::rint不同于std::round在这中间的情况是四舍五入，而不是远离零。
例
二次
#include <iostream>
#include <cmath>
#include <cfenv>
#include <climits>
int main()
{
#pragma STDC FENV_ACCESS ON
std::fesetround(FE_TONEAREST
std::cout << "rounding to nearest (halfway cases to even):\n"
<< "rint(+2.3) = " << std::rint(2.3)
<< " rint(+2.5) = " << std::rint(2.5)
<< " rint(+3.5) = " << std::rint(3.5) << '\n'
<< "rint(-2.3) = " << std::rint(-2.3)
<< " rint(-2.5) = " << std::rint(-2.5)
<< " rint(-3.5) = " << std::rint(-3.5) << '\n';
std::fesetround(FE_DOWNWARD
std::cout << "rounding down:\n"
<< "rint(+2.3) = " << std::rint(2.3)
<< " rint(+2.5) = " << std::rint(2.5)
<< " rint(+3.5) = " << std::rint(3.5) << '\n'
<< "rint(-2.3) = " << std::rint(-2.3)
<< " rint(-2.5) = " << std::rint(-2.5)
<< " rint(-3.5) = " << std::rint(-3.5) << '\n'
<< "rounding down with lrint\n"
<< "lrint(+2.3) = " << std::lrint(2.3)
<< " lrint(+2.5) = " << std::lrint(2.5)
<< " lrint(+3.5) = " << std::lrint(3.5) << '\n'
<< "lrint(-2.3) = " << std::lrint(-2.3)
<< " lrint(-2.5) = " << std::lrint(-2.5)
<< " lrint(-3.5) = " << std::lrint(-3.5) << '\n';
std::cout << "lrint(-0.0) = " << std::lrint(-0.0) << '\n'
<< "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";
}
二次
可能的产出：
二次
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) = 3
rint(-2.3) = -3 rint(-2.5) = -3 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
lrint(-0.0) = 0
lrint(-Inf) = -9223372036854775808
std::rint(0.1) = 0
FE_INEXACT was raised
std::lrint(LONG_MIN-2048.0) = -9223372036854775808
FE_INVALID was raised
二次
另见
| trunc (C++11) | nearest integer not greater in magnitude than the given value (function) |
|---|---|
| nearbyint (C++11) | nearest integer using current rounding mode (function) |
| fegetroundfesetround (C++11)(C++11) | gets or sets rounding direction (function) |
c Rint文件
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