c# – 为什么.NET Math.Round方法在处理负值时向下舍入为5而不向上？

我注意到,当我调用Math.Round并为其提供-0.375的十进制值并尝试将其四舍五入到两位小数时,它会将值四舍五入为-0.38.我总是被教导,5或更大的意思是向上舍入,这意味着它应该是-0.37.舍入到-0.37是 Javascript如何做到这一点,这就是我发现这个问题的方法.

这是一些示例代码.

decimal negNumber = -0.375m;
    var resultToEven = Math.Round(negNumber,2,MidpointRounding.ToEven);
    var resultAwayFromZero = Math.Round(negNumber,MidpointRounding.AwayFromZero);
    Console.WriteLine("Original Number: " + negNumber);
    Console.WriteLine("ToEven: " + resultToEven);
    Console.WriteLine("Away from zero: " + resultAwayFromZero);

这是它输出的内容.

Original Number: -0.375
ToEven: -0.38
Away from zero: -0.38

我使用的是.NET 4.0.

解决方法

Math.Round中的默认行为是使用 MidpointRounding.ToEven,它向“最接近的偶数”舍入.

MSDN describes why this was chosen：

If the digit in the digits position is odd,it is changed to an even digit. Otherwise,it is left unchanged. This behavior follows IEEE Standard 754,section 4. It is sometimes called rounding to nearest,or banker’s rounding. It minimizes rounding errors that result from consistently rounding a midpoint value in a single direction.

您的第二个电话使用AwayFromZero,它明确地舍入：

toward the nearest number that is away from zero

在您的情况下,-0.38比0.0更远离-0.37.