How to Initialize a `std::vector` from a C-style Array Efficiently?

Efficient Initialization of std::vector from C-style Array

When working with legacy code or external dependencies, you may encounter scenarios where data is provided as C-style arrays. Integrating this data into modern C structures like std::vector requires careful consideration for efficiency.

In the provided code snippet, the Foo class possesses a std::vector named w_. To populate this vector with data supplied as a C-style array (w with length len), you need a cost-effective method.

Avoid Excessive Resizing and Copying

While you could resize w_ to len and manually populate it, this approach involves unnecessary resizing and element-by-element copying. Similarly, using std::copy() introduces an extra copy operation.

Leverage Pointer Arithmetic

A more efficient solution is to utilize pointer arithmetic. Since pointers can be treated as iterators, you can initialize w_ directly using the range [w, w len):

w_.assign(w, w + len);

This syntax initializes w_ by assigning a range of elements from the C-style array w to its end. The std::vector class takes care of allocating the necessary memory and copying the elements efficiently.

By employing this method, you avoid the overhead of explicit resizing and separate copy operations, resulting in a more efficient and concise approach.

The above is the detailed content of How to Initialize a `std::vector` from a C-style Array Efficiently?. For more information, please follow other related articles on the PHP Chinese website!