How Can Boost::adaptors::reverse Enable Reverse Range-Based For-Loops in C 11?

C 11 Reverse Range-Based For-Loop Using Boost

Iterating through containers in reverse order can be achieved using a dedicated container adapter that reverses the direction of iterators. This allows us to implement reverse iteration with the convenience of range-based for-loops.

Fortunately, Boost provides such an adapter: boost::adaptors::reverse. This adapter takes a container as input and returns a new container adapter with reversed iterators.

To demonstrate its usage, consider the following example:

#include <list>
#include <iostream>
#include <boost/range/adaptor/reversed.hpp>

int main()
{
    std::list<int> x = {2, 3, 5, 7, 11, 13, 17, 19};
    for (auto i : boost::adaptors::reverse(x))
        std::cout << i << '\n';
    for (auto i : x)
        std::cout << i << '\n';
}

This code first creates a list x of integers. Then it iterates over the list in reverse order using the boost::adaptors::reverse(x) adapter. It prints the elements in reverse order, followed by the original order for comparison.

The output of the program is:

19
17
13
11
7
5
3
2
2
3
5
7
11
13
17
19

This demonstrates the ability of the Boost boost::adaptors::reverse adapter to reverse the direction of iterators and allow for convenient reverse iteration with range-based for-loops in C .

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