C ++ new int [0] - 它会分配内存吗？ [英] C++ new int[0] -- will it allocate memory?

问题描述

一个简单的测试应用程式：

A simple test app:

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

输出：

0x876c0b8

标准是什么说的？

推荐答案

从5.3.4 / 7

From 5.3.4/7

当direct-new-declarator中的表达式的值为零时，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.

从3.7.3.1/2

From 3.7.3.1/2

取消引用的效果作为零大小请求返回的指针未定义。

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

此外

即使请求的空间大小为[by new]，也可能会导致请求失败。

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

这意味着你可以做到，但是你不能合法地（在所有平台上以良好定义的方式）取消引用你获得的内存 - 你只能将它传递给数组删除 - 你应该删除它。

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，但包括用于说明目的）附加到从3.7.3.1/2的句子

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。目的是让操作符new（）可以通过调用malloc（）或calloc（）实现，所以规则基本上是相同的。 C ++与C不同，需要一个零请求来返回一个非空指针。]

[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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