有什么用0长度数组（或std ::数组）的？ [英] What is the use of 0-length array (or std::array)?

问题描述

在C ++ 11它允许你创建一个 0 长度C数组和 STD：阵列这样的

  INT ARR1 [0];
的std ::阵列ARR2＆LT; INT，0取代;
 

1. 所以我想那是什么没有一个空间来存储使用数组？


2. 其次什么是零长度数组？如果它是一个指针，在那里它指向？

解决方案

您第一个例子是不是标准的C ++，但的扩展的两个 GCC 和铛允许，它的版本灵活的阵列这回答问题：是灵活的阵列成员真的有必要解释此功能的诸多优点？如果您使用 -pedantic 标志，你会收到以下警告在 GCC ：

  

警告：ISO C ++禁止零大小的数组ARR1[-Wpedantic]

和铛以下警告：

  

警告：零大小的数组是一个扩展[-Wzero长度阵列]

至于你的第二个案例零长度的std ::阵列允许简单的泛型算法，无需特殊情况下的零长度的，例如类型的模板非类型参数的为size_t 的。至于性病::阵列的 CP preference节指出这是一个特殊情况：

  

有为零长度数组（N == 0）的特殊情况。在这种情况下，array.begin（）== array.end（），它是一些独特的价值。调用一个零大小的阵列上前方（）或背面（）的效果是不明确的。

这也使其与其他序列容器一致从而可以也是空。

In C++11 it allows you to create a 0 length C array and std:array like this:

int arr1[0];
std::array arr2<int,0>;

1. So I'm thinking what is the use of a array that doesn't have a space to store?
2. Secondly what is the zero length array? If it is a pointer, where does it pointing to?

解决方案

Your first example is not standard C++ but is an extension that both gcc and clang allow, it is version of flexible arrays and this answer to the question: Are flexible array members really necessary? explains the many advantages of this feature. If you compiled using the -pedantic flag you would have received the following warning in gcc:

warning: ISO C++ forbids zero-size array 'arr1' [-Wpedantic]

and the following warning in clang:

warning: zero size arrays are an extension [-Wzero-length-array]

As for your second case zero-length std::array allows for simpler generic algorithms without having to special case for zero-length, for example a template non-type parameter of type size_t. As the cppreference section for std::array notes this is a special case:

There is a special case for a zero-length array (N == 0). In that case, array.begin() == array.end(), which is some unique value. The effect of calling front() or back() on a zero-sized array is undefined.

It would also make it consistent with other sequence containers which can also be empty.

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