问题描述

一个简单的测试应用:

cout << new int[0] << endl;

输出:

0x876c0b8

所以看起来它有效.标准对此有何评论?分配"空内存块总是合法的吗?

So it looks like it works. What does the standard say about this? Is it always legal to "allocate" empty block of memory?

推荐答案

来自 5.3.4/7

当 direct-new-declarator 中表达式的值为零时，调用分配函数来分配一个没有元素的数组.

When the value of the expression in a direct-new-declarator is zero, the allocation function is called to allocate an array with no elements.

来自 3.7.3.1/2

From 3.7.3.1/2

取消引用作为零大小请求返回的指针的效果未定义.

The effect of dereferencing a pointer returned as a request for zero size is undefined.

还有

即使 [by new] 请求的空间大小为零，请求也可能失败.

Even if the size of the space requested [by new] is zero, the request can fail.

这意味着您可以这样做，但您不能合法地(在所有平台上以明确定义的方式)取消引用您获得的内存 - 您只能将其传递给数组删除 - 您应该删除它.

That means you can do it, but you can not legally (in a well defined manner across all platforms) dereference the memory that you get - you can only pass it to array delete - and you should delete it.

这是一个有趣的脚注(即不是标准的规范部分，但包含在说明中)附在 3.7.3.1/2 的句子中

Here is an interesting foot-note (i.e not a normative part of the standard, but included for expository purposes) attached to the sentence from 3.7.3.1/2

[32.目的是通过调用 malloc() 或 calloc() 来实现 operator new()，因此规则基本相同.C++ 与 C 的不同之处在于要求零请求返回非空指针.]

[32. The intent is to have operator new() implementable by calling malloc() or calloc(), so the rules are substantially the same. C++ differs from C in requiring a zero request to return a non-null pointer.]

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