std::array and std::vector are both container classes provided by the C++ Standard Library, but they have different characteristics and are used for different purposes:

  1. Size:
    • std::array: Has a fixed size determined at compile time, specified by its template parameter. Once created, the size of a std::array cannot be changed.
    • std::vector: Has a dynamic size that can grow or shrink at runtime. Elements can be added or removed from a std::vector after it’s created.
  2. Memory Allocation:
    • std::array: Typically allocated on the stack. The size of a std::array must be known at compile time, so its memory is allocated statically.
    • std::vector: Typically allocated on the heap. The memory for a std::vector is dynamically allocated, allowing it to resize as needed.
  3. Accessing Elements:
    • std::array: Supports constant time (O(1)) random access to elements using the [] operator. It provides efficient access to elements since the array is contiguous in memory.
    • std::vector: Supports constant time (O(1)) random access to elements using the [] operator. Like std::array, it provides efficient access to elements due to its contiguous memory layout.
  4. Performance:
    • std::array: Typically offers better performance than std::vector for small, fixed-size collections because of its static memory allocation and lack of dynamic resizing overhead.
    • std::vector: Offers better performance for large collections or when the size of the collection is unknown at compile time, as it can dynamically resize itself to accommodate new elements.
  5. Usage:
    • std::array: Useful when the size of the collection is known at compile time and does not change. It’s often used for small, fixed-size collections where the size is known in advance.
    • std::vector: Suitable when the size of the collection can change dynamically at runtime or when the size is not known at compile time. It’s a versatile container that can be resized and is widely used in C++.

In summary, choose std::array when you need a fixed-size container with known size at compile time, and choose std::vector when you need a dynamic-size container or when the size is not known at compile time.