[SOLVED] How to reverse a QList?

Issue

I see qCopy, and qCopybackward but neither seems to let me make a copy in reverse order. qCopybackward only copies it in reverse order, but keeps the darn elements in the same order! All I want to do is return a copy of the list in reverse order. There has to be a function for that, right?

Solution

If you don’t like the QTL, just use the STL. They might not have a Qt-ish API, but the STL API is rock-stable 🙂 That said, qCopyBackward is just std::copy_backward, so at least they’re consistent.

Answering your question:

template <typename T>
QList<T> reversed( const QList<T> & in ) {
    QList<T> result;
    result.reserve( in.size() ); // reserve is new in Qt 4.7
    std::reverse_copy( in.begin(), in.end(), std::back_inserter( result ) );
    return result;
}

EDIT 2015-07-21: Obviously (or maybe not), if you want a one-liner (and people seem to prefer that, looking at the relative upvotes of different answers after five years) and you have a non-const list the above collapses to

std::reverse(list.begin(), list.end());

But I guess the index fiddling stuff is better for job security 🙂

Answered By – Marc Mutz – mmutz

Answer Checked By – Willingham (BugsFixing Volunteer)