是对比较危险的是一个布尔？ [英] Is comparing a BOOL against YES dangerous?

问题描述

我发现了一个评论今天在源文件中：

I found a comment today in a source file:

//  - no longer compare BOOL against YES (dangerous!)

在Objective-C对比 BOOL 对是真的那么危险吗？为什么是这样？

Is comparing BOOL against YES in Objective-C really that dangerous? And why is that?

可以在运行时是变化的价值？也许 NO 总是 0 ，但是可 1 ， 2 或 3 - 根据运行时，编译器，你链接框架？

Can the value of YES change during runtime? Maybe NO is always 0 but YES can be 1, 2 or 3 - depending on runtime, compiler, your linked frameworks?

推荐答案

的问题是，BOOL是不是原生类型，而是一个typedef：

The problem is that BOOL is not a native type, but a typedef:

typedef signed char      BOOL;

#define YES             (BOOL)1
#define NO              (BOOL)0

作为一个字符，它的价值就不会被限制 TRUE 和 FALSE 。与另一个值会发生什么？

As a char, its values aren't constrained to TRUE and FALSE. What happens with another value?

BOOL b = 42;
if (b)
{
    // true
}
if (b != YES)
{
    // also true
}

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