比较双精度的奇怪行为，两个 PHP 双精度值不等价 [英] Odd behavior comparing doubles, two PHP double values aren't equivalent

问题描述

我在 PHP 中有两个看似相等的 double 值(至少在回显它们时).

I have two seemingly equal double values in PHP (at least when echoing them).

但是当将它们与双等号进行比较时，由于某种原因，它的评估结果为假.进行此类比较时是否有任何特殊注意事项?

But when comparing them with double equals, for some reason, it evaluates to false. Are there any special considerations when performing this kind of comparison?

推荐答案

您不应该使用 == 运算符比较浮点数.

You shouldn't compare floating point numbers using the == operator.

查看大警告和php 手册中的解释

有效的方法是断言这两个数字彼此之间存在一定的小距离，如下所示:

What will work is asserting that the two numbers are within a certain small distance of each other like this:

if(abs($a - $b) < 0.0001) {
    print("a is mostly equal to b");
}

原因是小数转换为二进制后再转换回十进制后进行浮点运算导致舍入错误.这些来回转换导致0.1 + 0.2不等于0.3的现象.

The reason is because of rounding errors due to floating point arithmetic performed after the decimals are converted to binary, then converted back to decimal. These back and forth conversions cause the phenomenon where 0.1 + 0.2 does not equal 0.3.

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