How Can I Easily Reverse Iterate Through a Container Using C 11 Range-Based For-Loops?

C 11 Reverse Range-Based For-Loops

Iterating over a container in reverse order with range-based for-loop requires reversing the direction of iterators. While explicit iterators provide a straightforward solution, is there a convenient container adapter that offers this functionality?

Reverse Iterator Adapter

Fortunately, the Boost library includes a solution: boost::adaptors::reverse. This adaptor reverses the iteration order of a container, enabling range-based for-loops to iterate in reverse.

Example Usage

Consider a container of integers:

std::list<int> x { 2, 3, 5, 7, 11, 13, 17, 19 };

To iterate over this container in reverse using a range-based for-loop, use the reverse adaptor:

for (auto i : boost::adaptors::reverse(x))
    std::cout << i << '\n';

This will print the elements of the list in reverse order.

Comparison to Original Iteration

For comparison, here is the original iteration order without the reverse adaptor:

for (auto i : x)
    std::cout << i << '\n';

This will print the elements of the list in their original order.

Conclusion

Boost's reverse adaptor provides a convenient way to iterate over a container in reverse order using range-based for-loops. This simplifies code and allows for more concise and efficient reverse iteration.

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