C++ new int[0]——它会分配内存吗？

Question

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。标准对此有何规定？ “分配”空内存块总是合法的吗？

Answer 1

来自 5.3.4/7

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

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

还有

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 - 您只能将它传递给数组 delete - 并且您应该删除它。

这是一个有趣的脚注(即不是标准的规范部分，但出于说明目的)附在 3.7.3.1/2 的句子上

[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.]