C ++如何避免浮点运算错误 [英] C++ How to avoid floating-point arithmetic error

问题描述

我正在写一个循环，它以浮点数递增，但是我遇到了一个浮点算术问题，如下例所示：

I am writing a loop that increments with a float, but I have come across a floating-point arithmetic issue illustrated in the following example:

for(float value = -2.0; value <= 2.0; value += 0.2)
    std::cout << value << std::endl;

这是输出：

-2
-1.8
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
1.46031e-07
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8

获取 1.46031e-07 而不是 0 ？我知道这与浮点错误有关，但我不知道为什么它正在发生，我应该做什么，以防止这种情况发生（如果有一种方式）。有人可以解释（或指向我的链接），将帮助我理解吗？任何输入是赞赏。谢谢！

Why exactly am I getting 1.46031e-07 instead of 0? I know this has something to do with floating-point errors, but I can't grasp why it is happening and what I should do to prevent this from happening (if there is a way). Can someone explain (or point me to a link) that will help me understand? Any input is appreciated. Thanks!

推荐答案

这是因为浮点数只具有一定的离散精度。

This is because floating point numbers have only a certain discrete precision.

0.2不是0.2，而是内部表示为稍微不同的数字。

The 0.2 is not really a 0.2, but is internally represented as a slightly different number.

这是为什么你看到一个差异。

That is why you are seeing a difference.

这在所有浮点计算中都很常见，你真的不能避免。

This is common in all floating point calculations, and you really can't avoid it.

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