Ranges Library

The C++20 algorithms library provides a number of useful functions for working with containers. There are two slightly different interfaces:

• Pre-C++20, we use iterator-based algorithms. These take a beginning and ending iterator into a container to work on.

  e.g.:

  auto it = std::find(vec.begin(), vec.end(), 42);
  

• In C++20, the ranges library was introduced. This provides functions that operate directly on containers.

  e.g.:

  auto it = std::ranges::find(vec, 42);
  

Tip

In C++, a range is anything that we can iterate over.

For viewing, transforming, and filtering a container, the ranges library is the more modern approach. There are some instances (like modifying the structure of the container) where we’ll use the iterator-based algorithms.

Note

For some algorithms, the ranges versions don’t come until standards after C++20. An example is summing the elements of a vector. In C++23, we could use std::ranges::fold_left(), but here we’ll use the iterator-based std::accumulate().

Algorithms

A list of the algorithms in the ranges library can be found on the cppreference.net constrained algorithms page

This includes algorithms that search through a container, check conditions on elements, and more. Many of these take a function to work with.

This also includes algorithms that change our container, transforming it, sorting it, etc.

Range adaptors

The ranges library also provides adaptors that can change how we view a sequence. We will look at this briefly.