What is the diffrence std::dynarray vs std:: vector ?

Comparison of std::dynarray and std::vector

In the C++ standard library, std::vector is a commonly used dynamic array container that can adjust its size dynamically as needed, offering great flexibility. On the other hand, std::dynarray was a proposed container for C++14 but was not adopted into the standard library. The design purpose of std::dynarray was to provide a fixed-size array where the size does not need to be fully specified at compile time, but once created, its size cannot be changed.

1. Definition and Initialization

• std::vector:

  cpp
  std::vector<int> v = {1, 2, 3, 4, 5};

• std::dynarray (if implemented):

  cpp
  std::dynarray<int> d(5); // Assuming the constructor parameter is the size

2. Size Variability

• std::vector: Can be dynamically changed in size at runtime. For example, you can use push_back, resize, etc., to add or remove elements.

  cpp
  v.push_back(6); // Now v contains {1, 2, 3, 4, 5, 6}

• std::dynarray: Once created, its size cannot be changed. This means there are no push_back or resize methods.

3. Performance Considerations

• std::vector: Because std::vector needs to dynamically increase capacity, it may incur additional memory allocation and copying overhead, which is particularly noticeable when resizing frequently.

• std::dynarray: Due to its fixed size, std::dynarray can avoid runtime memory allocation and copying, potentially offering better performance than std::vector, especially when the number of elements remains constant.

4. Use Cases

• std::vector: When you need a dynamically resizable array, std::vector is a good choice. For example, when reading an unknown quantity of input data.

• std::dynarray: If you know the array size in advance and it does not change during program execution, using a fixed-size container like std::dynarray can be more efficient. For example, when processing image data where the dimensions are fixed.

5. Conclusion

Overall, std::vector provides great flexibility and is suitable for various dynamic array scenarios. Although std::dynarray was not adopted into the C++ standard, its concept of fixed size offers advantages in specific cases. In C++, you can use the standard array std::array to achieve similar effects to std::dynarray, but the size of std::array must be specified at compile time.