处理浮点数的精度问题

问题描述

我想知道是否有一种方法来克服准确性问题，这似乎是我的机器的浮点数的内部表示的结果：

I was wondering if there is a way of overcoming an accuracy problem that seems to be the result of my machine's internal representation of floating-point numbers:

对于为了清楚起见，问题归纳为：

For the sake of clarity the problem is summarized as:

// str is "4.600";   atof( str ) is 4.5999999999999996
double mw = atof( str )

// The variables used in the columns calculation below are:
//
//                    mw = 4.5999999999999996
//                    p = 0.2
//                    g = 0.2
//                    h = 1 (integer)

int columns = (int) ( ( mw - ( h * 11 * p ) ) / ( ( h * 11 * p ) + g ) ) + 1;

在转换为整数类型之前，列计算的结果为1.9999999999999996;所以距离所期望的2.0的结果很近。

Prior to casting to an integer type the result of the columns calculation is 1.9999999999999996; so near yet so far from the desired result of 2.0.

任何建议最受欢迎。

推荐答案

将浮点数舍入为整数的非常简单有效的方法：

A very simple and effective way to round a floating point number to an integer:

int rounded = (int)(f + 0.5);

注意：只有 f 总是积极的。 （感谢j随机黑客​​）

Note: this only works if f is always positive. (thanks j random hacker)

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