"=！"代表什么?接线员呢? [英] What does the "=!" operator do?

问题描述

我不小心键入了=!而不是!=，这导致了一段时间内未被检测到的系统中的一个巨大错误；从那以后我已经修复了它，但是我对=!的作用感到好奇.

I accidentally typed =! instead of != that caused a huge bug in a system that went undetected for a while; I have fixed it since but I'm curious as to what =! does.

我有这样的东西

void foo(int param)
{
    int a = 0;

    ... 

    if (a =! param)
    {
        // never got here even when `a` was not equal to `param`  
    }
    ...
}

有人可以解释上面的if语句正在评估什么吗?

Can someone explain what the above if statement is evaluating ?

推荐答案

此表达式:

a =! param

将值!param分配给a. !param是在布尔上下文中求值的参数的否定版本.

assigns the value !param to a. !param is negated version of param evaluated in boolean context.

赋值运算符返回右侧的值，因此，如果!param为true，则if (a = !param)也会执行if主体.

Assignment operators return the value of the right hand side, so, if (a = !param) also executes the if body, if !param is true.

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