Mastering memory efficiency with std::span

A useful C++20 tool for providing a non-owning view of contiguous memory

Before diving into the usage of std::span, it is important to understand the concept of ownership of resources. When a container such as a std::vector is created, the container has ownership of the memory used to store data inside of it, meaning that it is the responsibility of the container to manage the lifecycle of this memory. Let’s look at a few common scenarios where a std::vector is used and determine if the ownership is affected:

• Viewing data in a container:

int main() {
  std::vector<int> myVector{1, 2, 3};
  for (const auto& value : myVector) {
    std::cout << value << " ";
  }
  std::cout << std::endl;
}

// Output:
// 1 2 3 

In this example, a range-based for loop is used to iterate over myVector in the main function. Here, myVector has ownership of the memory used to store the data — The creation of the std::vector allocated memory, which will be deallocated when main exits. Iterating over myVector doesn’t affect ownership of the container.

const auto& is used within the for loop for improved efficiency and best practices — const indicates that value should not be modified, auto lets the compiler deduce the type, and the & symbol turns value into a reference instead of an unnecessary copy of data.

• Passing a container by value:

int…