什么时候将数组转换为指针? [英] When are arrays converted to pointers?

问题描述

考虑以下计算数组长度的简单示例:

Consider the following simple example computing lenght of an array:

#include <iostream>

int a[] = {1, 2, 4};

int main(){ std::cout << sizeof(a)/sizeof(a[0]) << std::endl; }

演示

标准N4296::8.3.4/7 [dcl.array]

如果E是一个秩为i×j×的n维数组...×k，然后E出现在是受制于数组到指针转换的表达式中(4.2) 被转换为一个指向 (n-1) 维数组的指针等级 j ×...×k.

If E is an n-dimensional array of rank i×j×. . .×k, then E appearing in an expression that is subject to the array-to-pointer conversion (4.2) is converted to a pointer to an (n−1)-dimensional array with rank j ×. . .×k.

N4296::4.2/1 [conv.array]

N T 数组"或未知边界数组"类型的左值或右值of T"可以转换为指向 T 的指针"类型的纯右值.结果是指向数组第一个元素的指针.

An lvalue or rvalue of type "array of N T" or "array of unknown bound of T" can be converted to a prvalue of type "pointer to T". The result is a pointer to the first element of the array.

那么作为转换主题的表达式是什么?看起来未计算的操作数不是主题.

So what is the expressions which are the subject of the convertion? Looks like unevaluated operands are not the subject.

http://coliru.stacked-crooked.com/a/36a1d02c7feff41c

推荐答案

我知道以下表达式，其中数组不会转换/衰减为指针.

I know of the following expressions in which an array is not converted/decayed to a pointer.

1. 在 sizeof 运算符中使用时:sizeof(array)
2. 在 addressof 运算符中使用时:&array
3. 当用于将引用绑定到数组时:int (&ref)[3] = array;.
4. 推导用于实例化模板的类型名时.
5. 在decltype中使用时:decltype(array)

1. When used in a sizeof operator: sizeof(array)
2. When used in an addressof operator: &array
3. When used to bind a reference to an array: int (&ref)[3] = array;.
4. When deducing the typename to be used for instantiating templates.
5. When used in decltype: decltype(array)

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