std::rint, std::lrint, std::llrint

 

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常用数学函数

函数
基础操作
abs(int)labsllabsimaxabs (C++11) abs(float)fabs divldivlldivimaxdiv (C++11) fmod	remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nannanfnanl (C++11) (C++11) (C++11)
指数函数
exp exp2 (C++11) expm1 (C++11)	log log10 log1p (C++11) log2 (C++11)
幂函数
sqrt cbrt (C++11)	hypot (C++11) pow
三角与双曲函数
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C++11) acosh (C++11) atanh (C++11)

误差与伽马函数
erf (C++11) erfc (C++11)	lgamma (C++11) tgamma (C++11)
临近整数的浮点运算
ceil floor roundlroundllround (C++11) (C++11) (C++11)	trunc (C++11) nearbyint (C++11) rintlrintllrint (C++11) (C++11) (C++11)
浮点操作函数
ldexp scalbnscalbln (C++11) (C++11) ilogb (C++11) logb (C++11)	frexp modf nextafternexttoward (C++11) (C++11) copysign (C++11)
分类/比较
fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11)	isgreater (C++11) isgreaterequal (C++11) isless (C++11) islessequal (C++11) islessgreater (C++11) isunordered (C++11)
宏常量
HUGE_VALFHUGE_VALHUGE_VALL (C++11) (C++11) INFINITY (C++11) NAN (C++11) math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C++11) (C++11) (C++11) (C++11) (C++11)

 

定义于头文件 <cmath>
int rint( float arg );		(C++11 起)
int rint( double arg );		(C++11 起)
int rint( long double arg );		(C++11 起)
int rint( Integral arg );		(C++11 起)
long lrint( float arg );		(C++11 起)
long lrint( double arg );		(C++11 起)
long lrint( long double arg );		(C++11 起)
long lrint( Integral arg );		(C++11 起)
long long llrint( float arg );		(C++11 起)
long long llrint( double arg );		(C++11 起)
long long llrint( long double arg );		(C++11 起)
long long llrint( Integral arg );		(C++11 起)

舍入浮点参数arg一个整数值，浮点格式，使用当前的舍入模式。如果结果是不同的arg（即arg已经不是一个整数值），的浮点异常FE_INEXACT，提高.

原文：

Rounds the floating-point argument arg to an integer value in floating-point format, using the current rounding mode. If the result differs from arg (i.e., arg was not an integer value already), the floating-point exception FE_INEXACT is raised.

文本通过谷歌翻译机器翻译。
你可以帮忙校正和验证翻译。点击此处查看指示。

参数

arg

-

浮点值 原文： floating point value 文本通过谷歌翻译机器翻译。 你可以帮忙校正和验证翻译。点击此处查看指示。

返回值

的整数结果四舍五入arg

原文：

The integer result of rounding arg

文本通过谷歌翻译机器翻译。
你可以帮忙校正和验证翻译。点击此处查看指示。

注释

唯一的区别std::nearbyint和std::rint的是，std::rint可以提高FE_INEXACT浮点异常，而std::nearbyint不会提高.

原文：

The only difference between std::nearbyint and std::rint is that std::rint may raise the FE_INEXACT floating-point exception, while std::nearbyint never raises it.

文本通过谷歌翻译机器翻译。
你可以帮忙校正和验证翻译。点击此处查看指示。

示例

运行此代码

#include <cmath>
#include <cfenv>
#include <iostream>
int main()
{
    #pragma STDC FENV_ACCESS ON
    std::fesetround(FE_DOWNWARD);
    std::cout << "rounding using FE_DOWNWARD:\n" << std::fixed
              << " 12.0 ->  " << std::rint(12.0) << '\n'
              << " 12.1 ->  " << std::rint(12.1) << '\n'
              << "-12.1 -> " << std::rint(-12.1) << '\n'
              << " 12.5 ->  " << std::rint(12.5) << '\n'
              << " 12.9 ->  " << std::rint(12.9) << '\n'
              << "-12.9 -> " << std::rint(-12.9) << '\n'
              << " 13.0 ->  " << std::rint(13.0) << '\n';
    std::fesetround(FE_TONEAREST);
    std::cout << "rounding using FE_TONEAREST: \n"
              << " 12.0 ->  " << std::rint(12.0) << '\n'
              << " 12.1 ->  " << std::rint(12.1) << '\n'
              << "-12.1 -> " << std::rint(-12.1) << '\n'
              << " 12.5 ->  " << std::rint(12.5) << '\n'
              << " 12.9 ->  " << std::rint(12.9) << '\n'
              << "-12.9 -> " << std::rint(-12.9) << '\n'
              << " 13.0 ->  " << std::rint(13.0) << '\n';
 
    std::cout << "When rounding 12.0 ";
    std::feclearexcept(FE_ALL_EXCEPT);
    std::rint(12.0);
    if(std::fetestexcept(FE_ALL_EXCEPT) & FE_INEXACT) {
        std::cout << "inexact result reported\n";
    } else {
        std::cout << "inexact result not reported\n";
    }
 
    std::cout << "When rounding 12.1 ";
    std::rint(12.1);
    if(std::fetestexcept(FE_ALL_EXCEPT) & FE_INEXACT) {
        std::cout << "inexact result reported\n";
    } else {
        std::cout << "inexact result not reported\n";
    }
}

输出：

rounding using FE_DOWNWARD:
 12.0 ->  12.000000
 12.1 ->  12.000000
-12.1 -> -13.000000
 12.5 ->  12.000000
 12.9 ->  12.000000
-12.9 -> -13.000000
 13.0 ->  13.000000
rounding using FE_TONEAREST: 
 12.0 ->  12.000000
 12.1 ->  12.000000
-12.1 -> -12.000000
 12.5 ->  12.000000
 12.9 ->  13.000000
-12.9 -> -13.000000
 13.0 ->  13.000000
When rounding 12.0 inexact result not reported
When rounding 12.1 inexact result reported

另请参阅

nearbyint (C++11)	使用当前舍入模式的最接近整数 (函数)
trunc (C++11)	绝对值不大于给定值的最接近整数 (函数)
fegetround fesetround (C++11) (C++11)	获取或设置舍入方向 (函数)