C++ Library - <span>

The <span> header in C++20, introduces the std::span class template, which provides a way to represent contiguous sequences of data, such as arrays or vectors, without copying or moving the data.

Unlike traditional containers (like std::vector or std::array), a span does not own the data it references. Instead, it offers a view, means it acts as a lightweight wrapper around existing data, making it ideal to use in the scenarios where we need to pass arrays without incurring the overhead of copying.

Including <span> Header

To include the <span> header in your C++ program, you can use the following syntax.

#include <span>

Functions of <span> Header

Below is list of all functions from <span> header.

Creating a Span from an Array

In the following example, we are going to create a span from a allocated array.

#include <iostream>
#include <span>
void a(std::span < int > x) {
   for (int b: x) {
      std::cout << b << " ";
   }
   std::cout << std::endl;
}
int main() {
   int array[] = {2,4,6,8};
   std::span < int > x(array);
   a(x);
   return 0;
}

Output

Output of the above code is as follows −

2 4 6 8 

Slicing a Span

Consider the following example, where are going to slice a span to create a view of a subset of its elements.

#include <iostream>
#include <span>
void a(std::span < int > x) {
   for (int b: x) {
      std::cout << b << " ";
   }
   std::cout << std::endl;
}
int main() {
   int array[] = {1,12,23,34,45};
   std::span < int > x(array);
   auto slice = x.subspan(2, 4);
   a(slice);
   return 0;
}

Output

Following is the output of the above code −

23 34 45 0