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

Understanding 2D std::array Initialization Syntax

When attempting to initialize a 2D array of type std::array, 2> using braces, you may encounter an error. This is because std::array is an aggregate that encapsulates a C-style array. To properly initialize it, both an outer brace pair is needed for the class itself and inner braces for the actual C array.

Consider the following example:

std::array<int, 3> a1 = {{1, 2, 3}}; // Valid initialization of a 1D array

Applying this concept to a 2D array:

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

In this example:

• The outer braces { } enclose the entire class initialization.
• The inner braces { { } } enclose the individual C array initializations.

The additional braces in the correct example allow the compiler to distinguish between the class initialization and the initialization of the contained array. This results in proper compilation and initialization of the 2D array.

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