Modern C++
- C++ course
- Advanced
- Lesson 80/83
- 6 min
Write data processing with modern C++ (concepts, ranges).
Data processing with modern C++
In this lesson we add the process_data method to Framework. This method is a template constrained with concepts and does chained filtering with ranges.
Example: template<std::integral T> int process_data(const std::vector<T>& data). Body: for (auto x : data | std::views::filter([](T v) { return v > 0; })) sum += x;. This filters positive values and sums them. The std::integral constraint accepts only integer types; std::views::filter produces a lazy view. We take the previous lesson's skeleton and add this method.
Chaining with ranges
Ranges lets you chain algorithms with the | operator. data | std::views::filter(pred) filters the data and gives a lazy view.
Example: data | std::views::filter([](T v) { return v > 0; }). This drops negative values. You then sum the result with a for loop. In old C++ you would need an intermediate vector with std::copy_if; with ranges there is no intermediate variable. This means more readable and more efficient code. The output accumulates below the previous lesson's "Project ready" line.
Practice Add the process_data method
Add template<std::integral T> int process_data(const std::vector<T>& data) to Framework. Its body should filter with data | std::views::filter([](T v) { return v > 0; }) and sum. In run define std::vector<int> data{1, -2, 3}; and print with std::cout << "sum: " << process_data(data);.
Starter code
#include <iostream>
#include <string>
#include <vector>
#include <ranges>
#include <algorithm>
#include <concepts>
class Framework {
public:
int run();
// Add the process_data template method (with integral concept)
};
int Framework::run() {
std::cout << "Project ready" << std::endl;
// Call process_data and print the result
return 0;
}
int main() {
Framework fw;
fw.run();
return 0;
}Sample solution
#include <iostream>
#include <string>
#include <vector>
#include <ranges>
#include <algorithm>
#include <concepts>
class Framework {
public:
int run();
template<std::integral T>
int process_data(const std::vector<T>& data);
};
template<std::integral T>
int Framework::process_data(const std::vector<T>& data) {
int sum = 0;
for (auto x : data | std::views::filter([](T v) { return v > 0; })) {
sum += x;
}
return sum;
}
int Framework::run() {
std::cout << "Project ready" << std::endl;
std::vector<int> data{1, -2, 3};
std::cout << "sum: " << process_data(data);
return 0;
}
int main() {
Framework fw;
fw.run();
return 0;
}Expected output
Project ready sum: 4
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match each concept to its description
| Term | Meaning |
|---|---|
std::integral |
Integer constraint |
std::views::filter |
Filter view |
ranges |
Chained algorithms |
concept |
Type constraint |
2 the views filter
data | std::____::filter([](int v) { return v > 0; })data | std::views::filter([](int v) { return v > 0; })Explanation: std::views::filter produces a filter view.
3 What does std::ranges provide?
- Exception safety
- Multithreading
- Memory management
- Chaining composition of algorithms Correct answer
Explanation: ranges lets you chain algorithms with |.