数组指针运算 - 法律和未定义行为

问题描述

限时删除！！

我问自己，如果这些线code的可以在C和用C产生不确定的行为++。
我试着回答每一个点读什么标准说有关数组下标（C 6.5.6 - 8）。我没有贴全款，因为它是pretty长。

   1  int a[10];
   2  int b = a[9]; // ok
   3  int c = a[10]; // UB
   4  int* d = (a + 10); // ok
   5  int* e = &a[10]; // ok from C99 (& and [] are ignored, pointer is not deferenced), // UB in pre C99
   6  int* f = &a[11]; // ok from C99, UB in pre c99
      int* g = a;
   7  int* h = g + 15; // ok

I think that the same aswers should be valid for C++

Are these lines valid in C and in C++, have I misunderstood the standard?

解决方案

Neither 6 nor 7 are valid, because they do not perform pointer arithmetic inside an existing array (including the one-past-the-end pointer). Everything else is essentially correct.

In C only: Given that a[i] is identical to *(a + i), and &*p is always just p without evaluating *p, 5 should always be fine, although you're right that C89 does not specify this and this was only added in C99. (This is not true at all in C++, where operators can be overloaded and there is no mention of combining & and *.)

From n1570 (draft to C11), in paragraph 8 of 6.5.6 Additive operators:

C++ contains very similar wording (e.g. C++11, 5.7/5).

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