CppHow-ToBeginner · 3 min read

How to Use Ranges in C++: Syntax and Examples

In C++, ranges are used to work with sequences of elements more easily using the std::ranges library introduced in C++20. You can use range-based for loops, views, and algorithms that accept ranges to write cleaner and more expressive code.

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Syntax

The basic syntax for using ranges involves range-based for loops and the std::ranges library functions. A range is any object that has a beginning and an end, like containers or views.

for (auto& element : range) { ... } — iterates over elements in the range.
std::ranges::views — creates lazy views over ranges.
std::ranges::algorithm — algorithms that accept ranges directly.

cpp

for (auto& element : range) {
    // use element
}

// Using ranges algorithms
#include <ranges>
#include <vector>

std::vector<int> v = {1, 2, 3, 4, 5};
auto filtered = v | std::ranges::views::filter([](int n) { return n % 2 == 0; });

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Example

This example shows how to use a range-based for loop and std::ranges::views::filter to iterate over even numbers in a vector.

cpp

#include <iostream>
#include <vector>
#include <ranges>

int main() {
    std::vector<int> numbers = {1, 2, 3, 4, 5, 6};

    // Create a view that filters even numbers
    auto even_numbers = numbers | std::ranges::views::filter([](int n) { return n % 2 == 0; });

    std::cout << "Even numbers:";
    for (int n : even_numbers) {
        std::cout << ' ' << n;
    }
    std::cout << '\n';

    return 0;
}

Output

Even numbers: 2 4 6

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Common Pitfalls

Common mistakes when using ranges include:

Not including the <ranges> header.
Trying to use ranges features in C++ versions before C++20.
Forgetting that views are lazy and do not store data themselves.
Using range-based for loops on objects that are not ranges.

cpp

#include <iostream>
#include <vector>
// Missing <ranges> header

int main() {
    std::vector<int> v = {1, 2, 3};
    // This will cause a compile error because views are not available
    // auto filtered = v | std::ranges::views::filter([](int n) { return n > 1; });

    // Correct way: include <ranges> and compile with C++20
    return 0;
}

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Quick Reference

Range-based for loop: for (auto& x : range) { ... }

Filter view: auto filtered = range | std::ranges::views::filter(predicate);

Transform view: auto transformed = range | std::ranges::views::transform(func);

Common algorithms: std::ranges::sort(range); std::ranges::find(range, value);

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Key Takeaways

Ranges in C++20 simplify working with sequences using views and range-based for loops.

Always include and compile with C++20 or later to use ranges features.

Views are lazy and do not copy data; they create a transformed view of the original range.

Use std::ranges algorithms directly on ranges for cleaner and safer code.

Common views include filter, transform, and take, which help process data efficiently.