Copying from Generated Ranges
Can these copy algorithms be used with input ranges that are generated on-the-fly, such as from a generator function?
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.
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().