C++ Library - <span>

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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.

Sr.No	Functions & Description
1	operator= It assigns a span.
2	begin It returns an iterator to the beginning.
3	cbegin It returns an constant iterator to the beginning.
4	end It returns an iterator to the end.
5	cend It returns an constant iterator to the end.
6	rbegin It returns a reverse iterator to the beginning.
7	crbegin It returns a constant reverse iterator to the beginning.
8	rend It returns a reverse iterator to the end.
9	crend It returns a constant reverse iterator to the end.
10	front It access the first element.
11	back It access the last element.
12	at It access specified element with bounds checking.
13	operator[] It access specified element.
14	data It direct access to the underlying contiguous storage.
15	size It returns the number of elements.
16	size_bytes It returns the size of the sequence in bytes.
17	empty It checks if the sequence is empty.
18	first It obtains a subspan consisting of the first N elements of the sequence.
19	last It obtains a subspan consisting of the last N elements of the sequence.
20	subspan It obtains a subspan.

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