Using Sentinels with Standard Algorithms in C++

Sentinels can be integrated with standard algorithms in C++ to provide more flexible termination conditions. Standard algorithms such as std::ranges::for_each() can accept both iterators and sentinels, allowing you to define when an algorithm should stop processing elements.

Here’s an example of using a sentinel with std::ranges::for_each():

1#include <algorithm>
2#include <iostream>
3#include <vector>
4
5struct Sentinel {
6  bool operator==(
7    std::vector<int>::const_iterator iter) const {
8    return *iter < 0;
9  }
10};
11
12void Log(int x) { std::cout << x << ", "; }
13
14int main() {
15  std::vector<int> numbers{1, 4, 3, 8, -2, 5};
16  Sentinel s;
17
18  std::ranges::for_each(numbers.begin(), s, Log);
19}

11, 4, 3, 8,

In this example, std::ranges::for_each() iterates through the vector and logs each element until it encounters the first negative number, as specified by the custom sentinel.

Using sentinels with standard algorithms allows for more complex and expressive termination conditions, making your algorithms more flexible and powerful. By defining custom sentinels, you can tailor the behavior of standard algorithms to suit your specific needs.