无意中使用 = 而不是 ==

Inadvertent use of = instead of ==(无意中使用 = 而不是 ==)

问题描述

好像

if (x=y) { .... }

而不是

if (x==y) { ... } 

是万恶之源.

为什么不所有编译器将其标记为错误而不是可配置的警告?

Why don't all compilers mark it as error instead of a configurable warning?

我有兴趣找出构造 if (x=y) 有用的情况.

I'm interested in finding out cases where the construct if (x=y) is useful.

推荐答案

大多数时候，编译器都在努力保持向后兼容.

Most of the time, compilers try very hard to remain backward compatible.

改变他们在这件事上的行为以引发错误将破坏现有的合法代码，甚至开始引发有关它的警告也会导致自动系统出现问题，这些系统通过自动编译并检查错误和警告来跟踪代码.

Changing their behavior in this matter to throw errors will break existing legit code, and even starting to throw warnings about it will cause problems with automatic systems that keep track of code by automatically compiling it and checking for errors and warnings.

这是一个我们几乎被 atm 困住的邪恶，但有一些方法可以规避和减少它的危险.

This is an evil we're pretty much stuck with atm, but there are ways to circumvent and reduce the dangers of it.

例子:

   void *ptr = calloc(1, sizeof(array));
   if (NULL = ptr) {
       // some error
   }

这会导致编译错误.

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