Yes, these copy algorithms can be used with input ranges that are generated on-the-fly, such as from a generator function. The key is to create an iterator that generates values as needed and supports the necessary iterator interface.
Generator Function
Here’s an example of a generator function that produces an infinite sequence of numbers, and how you can use it with std::ranges::copy_n():
#include <algorithm>
#include <iostream>
#include <vector>
#include <iterator>
class InfiniteSequence {
public:
InfiniteSequence(int start) : current(start) {}
int operator()() {
return current++;
}
private:
int current;
};
int main() {
InfiniteSequence generator(1);
std::vector<int> Destination(10);
std::generate_n(
Destination.begin(), 10, generator);
for (int Value : Destination) {
std::cout << Value << ", ";
}
}1, 2, 3, 4, 5, 6, 7, 8, 9, 10,Using Custom Iterators
To create an input range that can be used with std::ranges::copy() or other algorithms, you can define a custom iterator that generates values on-the-fly. Here’s an example:
#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
class GeneratorIterator {
public:
using iterator_category = std::input_iterator_tag;
using value_type = int;
using difference_type = std::ptrdiff_t;
using pointer = int*;
using reference = int&;
GeneratorIterator(int start) : current(start) {}
int operator*() const { return current; }
GeneratorIterator& operator++() {
++current;
return *this;
}
GeneratorIterator operator++(int) {
GeneratorIterator tmp = *this;
++current;
return tmp;
}
friend bool operator==(const GeneratorIterator& a,
const GeneratorIterator& b) {
return a.current == b.current;
}
friend bool operator!=(const GeneratorIterator& a,
const GeneratorIterator& b) {
return a.current != b.current;
}
private:
int current;
};
int main() {
GeneratorIterator start(1);
GeneratorIterator end(11); // End after generating 10 elements
std::vector<int> Destination(10);
std::copy(start, end, Destination.begin());
for (int Value : Destination) {
std::cout << Value << ", ";
}
}1, 2, 3, 4, 5, 6, 7, 8, 9, 10,Using a Generator Function Directly with std::ranges::copy()
You can also use a generator function directly with std::ranges::copy() by converting it into a range. Here’s how:
#include <algorithm>
#include <iostream>
#include <vector>
#include <ranges>
#include <iterator>
auto generate_infinite_sequence(int start) {
return std::views::iota(start);
}
int main() {
auto generator = generate_infinite_sequence(1);
std::vector<int> Destination(10);
std::ranges::copy_n(
generator.begin(), 10, Destination.begin());
for (int Value : Destination) {
std::cout << Value << ", ";
}
}1, 2, 3, 4, 5, 6, 7, 8, 9, 10,Key Points
- Custom Iterators: Define custom iterators to generate values on-the-fly.
- Compatibility: Ensure the iterator supports the necessary interface (
operator*,operator++, andoperator!=). - Flexibility: This approach allows you to generate values dynamically and use them with standard copy algorithms.
By using generator functions or custom iterators, you can effectively integrate on-the-fly input ranges with standard copy algorithms, making your code more flexible and powerful.
Answers to questions are automatically generated and may not have been reviewed.
Copying Algorithms
An introduction to the 7 copying algorithms in the C++ standard library: copy(), copy_n(), copy_if(), copy_backward(), reverse_copy(), rotate_copy(), and unique_copy().
