In C++11 it allows you to create a 0 length C array and std:array like this:
在c++ 11中，它允许创建一个0长度的C数组和std:数组，如下所示:
int arr1[0];
std::array arr2<int,0>;
- So I'm thinking what is the use of a array that doesn't have a space to store?
- 我在想一个没有空间存储的数组有什么用呢?
- Secondly what is the zero length array? If it is a pointer, where does it pointing to?
- 第二，什么是零长度数组?如果它是一个指针，它指向哪里?
1 个解决方案
#1
17
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:
您的第一个示例不是标准的c++，而是gcc和clang都允许的扩展，它是灵活数组的版本，这个问题的答案是:灵活数组成员真的有必要吗?说明此特性的许多优点。如果您使用-pedantic标志进行编译，您将在gcc中收到以下警告:
warning: ISO C++ forbids zero-size array 'arr1' [-Wpedantic]
警告:ISO c++禁止零大小的数组‘arr1’[-Wpedantic]
and the following warning in clang:
以下是在clang的警告:
warning: zero size arrays are an extension [-Wzero-length-array]
警告:0大小的数组是扩展名[- w零长度数组]
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:
对于第二个大小写零长度的std::array允许使用更简单的通用算法，而不必使用特殊大小写表示零长度，例如size_t类型的模板非类型参数。作为std:::array的cppreference部分，这是一个特例:
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.
对于长度为0的数组(N = 0)有一个特殊的情况，在这种情况下，array.begin() == array.end()是某个唯一值。调用front()或back()对一个零大小的数组的效果没有定义。
It would also make it consistent with other sequence containers which can also be empty.
它还可以使它与其他序列容器保持一致，这些容器也可以是空的。
#1
17
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:
您的第一个示例不是标准的c++，而是gcc和clang都允许的扩展，它是灵活数组的版本，这个问题的答案是:灵活数组成员真的有必要吗?说明此特性的许多优点。如果您使用-pedantic标志进行编译，您将在gcc中收到以下警告:
warning: ISO C++ forbids zero-size array 'arr1' [-Wpedantic]
警告:ISO c++禁止零大小的数组‘arr1’[-Wpedantic]
and the following warning in clang:
以下是在clang的警告:
warning: zero size arrays are an extension [-Wzero-length-array]
警告:0大小的数组是扩展名[- w零长度数组]
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:
对于第二个大小写零长度的std::array允许使用更简单的通用算法，而不必使用特殊大小写表示零长度，例如size_t类型的模板非类型参数。作为std:::array的cppreference部分，这是一个特例:
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.
对于长度为0的数组(N = 0)有一个特殊的情况，在这种情况下，array.begin() == array.end()是某个唯一值。调用front()或back()对一个零大小的数组的效果没有定义。
It would also make it consistent with other sequence containers which can also be empty.
它还可以使它与其他序列容器保持一致，这些容器也可以是空的。