将 BOOL 与 YES 进行比较是否危险?

Is comparing a BOOL against YES#160;dangerous?(将 BOOL 与 YES 进行比较是否危险?)

问题描述

我今天在一个源文件中发现了一条评论:

I found a comment today in a source file:

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

在 Objective-C 中比较 BOOL 和 YES 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?

YES 的值可以在运行时改变吗?也许 NO 总是 0 但 YES 可以是 1、2 或 >3 - 取决于运行时、编译器、链接的框架?

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

问题是BOOL不是原生类型，而是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，它的值不受 TRUE 和 FALSE 的限制.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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