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I found that there is a template partial specialisation in std::array for std::array<T, 0>.
template <typename T>
struct array<T, 0> {
//...
typedef typename conditional<is_const<_Tp>::value, const char,
char>::type _CharType;
struct _ArrayInStructT { _Tp __data_[1]; };
alignas(_ArrayInStructT) _CharType __elems_[sizeof(_ArrayInStructT)];
//...
}
So what is the purpose of implementing std::array<T, 0>?
Thanks very much!
700
std::array provides fixed array functionality that won't decay when passed into a function. std::array is defined in the <array> header, inside the std namespace. Just like the native implementation of fixed arrays, the length of a std::array must be known at compile time.
std::array::array For elements of a class type this means that their default constructor is called. For elements of fundamental types, they are left uninitialized (unless the array object has static storage, in which case they are zero-initialized).
std::array is a container that encapsulates fixed size arrays. This container is an aggregate type with the same semantics as a struct holding a C-style array T[N] as its only non-static data member. Unlike a C-style array, it doesn't decay to T* automatically.
std::array provides many benefits over built-in arrays, such as preventing automatic decay into a pointer, maintaining the array size, providing bounds checking, and allowing the use of C++ container operations.
The reason is, simply, uniformity. When you're writing templates it's much easier to be able to always write std::array<Ty, N> than to have to write a special case when N is 0. That kind of uniformity comes up often: new int[0], operator new(0), std::malloc(0), for (int i = 0; i < N; ++i) when N is 0.
110
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