将double转换为int的结果是错误的 [英] Result of casting double to int is wrong

问题描述

当我运行下面的代码似乎有一些晦涩的舍入错误：

  int roundedTotal = （PriorityJob * 100.0）; 
  

最初 PriorityJob = 1.4 和 roundedTotal 未定义。评估 PriorityJob * 100.0 此时给出 140 。之后 roundedTotal = 139 。

显然，140.0被解释为139.99999。这是浮点引擎的缺陷吗？

解决方案

几乎每个现代计算机都使用

正如 1/3 = 0.33333333。

... 不能精确表示为小数，因此 1/10 （因此大多数非整数十进制值，包括 1.4 ）不能精确表示为二进制小数。

您可能希望四舍五入为最接近的整数，而代之以最接近的可表示值，它可能稍微大于或小于true ：（int）（PriorityJob * 100.0 + 0.5）

There seems to be some kind of obscure rounding error when I run the following code:

int roundedTotal = (int)(PriorityJob * 100.0);

Initially PriorityJob = 1.4 and roundedTotal is undefined. Evaluating PriorityJob * 100.0 at that point gives 140. Afterwards roundedTotal = 139.

Apparently, 140.0 is being interpreted as 139.99999. Is this a deficiency in the floating point engine? I have never seen anything like it.

解决方案

Just about every modern computer uses a binary representation for floating-point numbers.

Just as 1/3 = 0.33333333... can't be represented exactly as a decimal fraction, so 1/10 (and hence most non-integer decimal values, including 1.4) can't be represented exactly as a binary fraction. It will instead be represented by the nearest representable value, which may be slightly more or less than the "true" value.

You might want to round to the nearest integer instead: (int)(PriorityJob * 100.0 + 0.5)

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