Why Does std::array Lack a Constructor with Value Initialization?

Why doesn't std::array have a Constructor with Value Initialization?

std::array is a class representing a fixed-size array, yet it lacks a constructor that takes a value for all its elements. The absence of such a constructor may seem puzzling, especially when dynamic containers like std::vector have similar constructors.

This omission is intentional, as std::array is designed as an aggregate type. Aggregates in C are classes that consist solely of data members and do not have user-declared constructors. As such, std::array can only be initialized with brace-enclosed initializer lists or through copy/move construction.

While std::array provides a fill method for assigning values to all elements, it's not a substitute for a constructor with value initialization. The fill method operates on an already-constructed array, initializing its elements but not affecting the memory state prior to construction.

If you need to initialize all elements of an std::array with a particular value (-1 in your example), you can use default construction followed by fill:

<code class="cpp">std::array<int, 10> myArray; // default construction (uninitialized memory)
myArray.fill(-1); // initialize all elements with -1</code>

Default construction won't zero out the memory for aggregates, so the fill method correctly initializes all elements without needing to overwrite zeroed values. Note that this behavior may change for non-trivially initializable types.

The above is the detailed content of Why Does std::array Lack a Constructor with Value Initialization?. For more information, please follow other related articles on the PHP Chinese website!