有YES / NO之间的差异，TRUE / ​​FALSE和真/假在Objective-C？ [英] Is there a difference between YES/NO,TRUE/FALSE and true/false in objective-c?

问题描述

简单的问题真的;有这些值之间的差（和有BOOL和布尔之间的差）？一位同事提到，他们评估在Objective-C的不同的事情，但是当我看着的typedef在各自的.h文件，YES / TRUE /真正的都被定义为 1 和NO / FALSE /假都定义为 0 。难道真有什么区别呢？

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

有没有实际的区别的的提供的使用 BOOL 变量布尔值。 ç流程的基础上，他们是否计算为0或布尔前pressions不是0，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) { ... }

意思是一样的。

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

这就是为什么你可以评估的任何基本类型或前pression为布尔测试（包括，例如指针）。需要注意的是你应该做前者，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，有 是的如果您分配钝值，所谓的 BOOL 变量和测试的差别为特定值，所以总是把它们作为布尔值，只有从他们的的#define 值分配。

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，从来没有测试使用的字符比较布尔 - 它不仅是危险的，因为 someVar 可能被分配一个非零值，这是不肯定的，但是，在我认为更重要的是，它没有前preSS的意图正确：

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!

在换句话说，使用的结构，因为他们的目的并记录被使用，你会从伤害的世界C备用自己。

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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