为NULL总是用C零？ [英] Is NULL always zero in C?

问题描述

昨天我面试一个中等水平的软件工程位置的家伙，他提到，C，NULL并不总是为零，他曾见过的C实现的，其中NULL不为零。我觉得这是高度怀疑，但我想是肯定的。任何人都知道，如果他是正确的？

I was interviewing a guy for a mid-level software engineering position yesterday, and he mentioned that in C, NULL is not always zero and that he had seen implementations of C where NULL is not zero. I find this highly suspect, but I want to be sure. Anyone know if he is right?

（回应将不会影响对这个人选我的判断，我已经提交了我的决定，我的经理。）

(Responses will not affect my judgement on this candidate, I've already submitted my decision to my manager.)

推荐答案

我假设你指的是空指针。它是保证比较等于 0 ¹ 不过，这并不必须重新presented具有全零比特。< SUP> 2

I'm assuming you mean the null pointer. It is guaranteed to compare equal to 0.¹ But it doesn't have to be represented with all-zero bits.²

还有 comp.lang.c常见问题解答参见空指针。

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1. 见C99，6.3.2.3。


2. 有没有明确的要求;但看到C99的注脚，7.20.3（感谢在评论@birryree）。
   

1. See C99, 6.3.2.3.
2. There's no explicit claim; but see the footnote for C99, 7.20.3 (thanks to @birryree in the comments).

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