Ranges
- C++ course
- Advanced
- Lesson 5/83
- 5 min
Learn composable algorithms with C++20 ranges.
Ranges
Ranges (C++20) is a composable view infrastructure in the <ranges> header. Views like std::views::filter and std::views::transform operate on a container without copying it.
The syntax is v | std::views::filter(pred) | std::views::transform(fn). The | operator chains views; each view takes the previous range as its source. The result is computed lazily during iteration, so no intermediate containers are created.
std::views::transform
std::views::transform applies a function to each element. Example: v | std::views::transform([](int x){ return x * x; }) squares each element. A filter | transform chain first filters, then transforms.
Transform does not modify the source container; it produces a new view. The view is computed during iteration, so there is no memory cost. Unlike the legacy std::transform algorithm, no intermediate container is required.
Practice Filter and transform
Create std::vector<int> v{1, 2, 3, 4, 5, 6};. Use v | std::views::filter to keep evens, then std::views::transform to map each to x * 10. Print each result via a for loop to std::cout.
Starter code
#include <iostream>
#include <vector>
#include <ranges>
int main() {
std::vector<int> v{1, 2, 3, 4, 5, 6};
// Filter and transform, then print
return 0;
}Sample solution
#include <iostream>
#include <vector>
#include <ranges>
int main() {
std::vector<int> v{1, 2, 3, 4, 5, 6};
auto r = v | std::views::filter([](int x){ return x % 2 == 0; })
| std::views::transform([](int x){ return x * 10; });
for (int x : r) std::cout << x;
return 0;
}Expected output
204060
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the chain operator
auto r = v ____ std::views::filter([](int x){ return x % 2 == 0; });auto r = v | std::views::filter([](int x){ return x % 2 == 0; });Explanation: The | operator chains views.
2 What does std::views::filter do?
- Keeps elements that match Correct answer
- Transforms each element
- Copies the container
- Sorts the container
Explanation: filter keeps elements where the predicate is true.
3 Match the view to its purpose
| Term | Meaning |
|---|---|
std::views::filter |
Filter by predicate |
std::views::transform |
Map each element |
std::views::take |
Take first n |
std::views::reverse |
Reverse order |