Does `std::array` Guarantee the Same Size and Memory Layout as a Regular C Array?

Guaranteed Semantics for std::array Size and Memory Layout

In C 11, std::array provides contiguous storage and performance comparable to regular arrays. However, the standard's requirements for std::array raise the question: does it necessarily have the same size and memory layout as an equivalent array?

According to §23.3.2.1/2 of the C standard, std::array is an aggregate initialized using an initializer list. Since aggregates cannot use constructors to convert data, the initializer-list must directly represent the values stored in the array.

This implies that the size of std::array must be determined by the number of elements specified in its template argument. Additionally, the memory layout should be identical to that of an array, without any auxiliary data or padding.

While the standard does not explicitly state this requirement, it is strongly implied by the aggregate nature of std::array and the mandate for contiguous storage.

This means that sizeof(std::array) should indeed be equal to sizeof(int) * N, ensuring that the examples given in the original inquiry will function as intended.

In practice, compilers and implementations typically adhere to this expected behavior. However, it is important to note that the standard does not strictly enforce it, leaving open the possibility of non-compliant implementations.

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