Handling Overlapping Ranges

When using std::ranges::move(), handling overlapping ranges can be tricky because it can lead to undefined behavior if not managed correctly.

The key is to ensure that the destination range does not overlap with the source range in a way that would overwrite elements that are yet to be moved.

Using std::ranges::move_backward()

One effective way to handle overlapping ranges is to use std::ranges::move_backward() instead of std::ranges::move().

This algorithm moves elements from right to left, which helps avoid overwriting elements that haven't been moved yet.

Here's an example:

1#include <algorithm>
2#include <iostream>
3#include <vector>
4
5int main() {
6  std::vector<int> values{1, 2, 3, 4, 5};
7
8  // Move elements two positions to the right
9  std::ranges::move_backward(values.begin(),
10                             values.begin() + 3,
11                             values.end());
12
13  for (const auto& value : values) {
14    std::cout << value << ", ";
15  }
16}

11, 2, 1, 2, 3,

In this example, move_backward() is used to shift elements to the right without causing overlap issues.

Guidelines

If moving left, use std::ranges::move():

1std::ranges::move(
2  container.begin() + 2,
3  container.end(),
4  container.begin()
5);

If moving right, use std::ranges::move_backward():

1std::ranges::move_backward(
2  container.begin(),
3  container.end() - 2,
4  container.end()
5);

Conclusion

When dealing with overlapping ranges, std::ranges::move_backward() is often the safer choice to ensure elements are moved correctly without causing undefined behavior.

By moving elements from right to left, it prevents the overwriting of elements that are yet to be moved.