Objective-c 中的 YES/NO,TRUE/FALSE 和 true/false 之间有区别吗? [英] Is there a difference between YES/NO,TRUE/FALSE and true/false in objective-c?

问题描述

真的很简单的问题；这些值之间是否存在差异(BOOL 和 bool 之间是否存在差异)?一位同事提到他们在 Objective-C 中评估不同的东西，但是当我查看他们各自的 .h 文件中的 typedef 时，YES/TRUE/true 都被定义为 1 和 NO/FALSE/false 都定义为 0.真的有区别吗?

Simple question really; is there a difference between these values (and is there a difference between BOOL and bool)? A co-worker mentioned that they evaluate to different things in Objective-C, but when I looked at the typedefs in their respective .h files, YES/TRUE/true were all defined as 1 and NO/FALSE/false were all defined as 0. Is there really any difference?

推荐答案

没有实际区别 provided 你使用 BOOL 变量作为布尔值.C 根据布尔表达式的计算结果是否为 0 来处理它们.所以:

There is no practical difference provided you use BOOL variables as booleans. C processes boolean expressions based on whether they evaluate to 0 or not 0. So:

if(someVar ) { ... }
if(!someVar) { ... }

意思相同

if(someVar!=0) { ... }
if(someVar==0) { ... }

这就是为什么您可以将任何原始类型或表达式评估为布尔测试(包括例如指针)的原因.注意你应该做前者，而不是后者.

which is why you can evaluate any primitive type or expression as a boolean test (including, e.g. pointers). Note that you should do the former, not the latter.

请注意，如果您将钝值分配给所谓的 BOOL 变量并测试特定值，则 会有所不同，因此总是将它们用作布尔值，并且仅从它们的 #define 值中分配它们.

Note that there is a difference if you assign obtuse values to a so-called BOOL variable and test for specific values, so always use them as booleans and only assign them from their #define values.

重要的是，永远不要使用字符比较来测试布尔值——这不仅有风险，因为 someVar 可能被分配一个非零值，这不是 YES，但在我看来，更重要的是，它失败了正确表达意图:

Importantly, never test booleans using a character comparison -- it's not only risky because someVar could be assigned a non-zero value which is not YES, but, in my opinion more importantly, it fails to express the intent correctly:

if(someVar==YES) { ... } // don't do this!
if(someVar==NO ) { ... } // don't do this either!

换句话说，按照预期使用和记录在案的方式使用构造，您将避免在 C 语言中受到伤害.

In other words, use constructs as they are intended and documented to be used and you'll spare yourself from a world of hurt in C.

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