比较浮点在目标C中的奇怪问题 [英] Strange problem comparing floats in objective-C

问题描述

在算法的某个时候，我需要比较一个类的属性的float值为float。所以我这样做：

At some point in an algorithm I need to compare the float value of a property of a class to a float. So I do this:

if (self.scroller.currentValue <= 0.1) {
}

其中currentValue是一个float属性。

where currentValue is a float property.

当我有相等和 self.scroller.currentValue = 0.1 if语句未被满足，代码未执行！我发现，我可以通过转换0.1来解决这个问题。像这样：

However, when I have equality and self.scroller.currentValue = 0.1 the if statement is not fulfilled and the code not executed! I found out that I can fix this by casting 0.1 to float. Like this:

if (self.scroller.currentValue <= (float)0.1) {
}

这很好。

我为什么会发生这种情况？

Can anyone explain to my why this is happening? Is 0.1 defined as a double by default or something?

推荐答案

我相信，没有找到这样的标准，当比较 float 到 double float 在比较前转换为 double 。没有修饰符的浮点数在C中被认为是 double

。

I believe, having not found the standard that says so, that when comparing a float to a double the float is cast to a double before comparing. Floating point numbers without a modifier are considered to be double in C.

然而，在C中没有精确0.1的浮点和双精度表示。现在，使用一个float给你一个小错误。使用double会给你一个更小的错误。现在的问题是，通过将 float 转换为 double c $ c> float 。

However, in C there is no exact representation of 0.1 in floats and doubles. Now, using a float gives you a small error. Using a double gives you an even smaller error. The problem now is, that by casting the float to a double you carry over the bigger of error of the float. Of course they aren't gone compare equal now.

而不是使用（float）0.1 ，你可以使用 0.1f 这是一个更好阅读。

Instead of using (float)0.1 you could use 0.1f which is a bit nicer to read.

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