How to Correctly Initialize a 2D `std::array` in C Using Braces?

Initialization of 2D std::array with Braces

While working with C , initializing a 2D std::array using braces can be challenging. The following code snippet illustrates the issue:

std::array<std::array<int, 3>, 2> a {
    {1, 2, 3},
    {4, 5, 6}
};

This approach fails to compile, with the compiler error indicating too many initializers for std::array, 2u>. To understand why this occurs, it's crucial to know the underlying implementation of std::array.

std::array Internals

std::array is an aggregate that encompasses a C-style array. Hence, to initialize it correctly, it requires outer braces for the class itself and inner braces for the C array member:

std::array<int, 3> a1 = { { 1, 2, 3 } };

Extending this logic to a 2D array results in the following valid initialization:

std::array<std::array<int, 3>, 2> a2 { { { {1, 2, 3} }, { { 4, 5, 6} } } };

In this example:

• "{ { {1, 2, 3} }, { { 4, 5, 6} } }" are the class braces, enclosing the initialization of the 2D array.
• "{{1, 2, 3}, {4, 5, 6}}" are the braces for the inner C-style arrays, initializing each row of the 2D array.

The above is the detailed content of How to Correctly Initialize a 2D `std::array` in C Using Braces?. For more information, please follow other related articles on the PHP Chinese website!