检查指针是否为空是否安全，然后在相同的if语句中取消引用它是否安全? [英] Is it safe to check if a pointer is null, then dereference it in the same if statement?

问题描述

如果传入空指针，以下代码是否安全?

Is the following code safe if a null pointer is passed in?

if(ptr && *ptr == value)
{
   //do something
}

检查的顺序重要吗?如果我将其更改为此可以正常工作吗?

Does the order of the checks matter? Does it work if I change it to this?

if(*ptr == value && ptr)
{
   //do something
}

推荐答案

前者是正确和安全的，后者则不是.

The former is correct and safe, the latter is not.

内置的&&运算符具有短路语义，这意味着当且仅当第一个为true时，才对第二个参数求值.

The built-in && operator has short-circuit semantics, meaning that the second argument is evaluated if and only if the first one is true.

(超载运算符不是这种情况.)

(This is not the case for overloaded operators.)

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