If we look at C++ standard library and its sequence containers (array, vector, list, forward_list, deque) we will notice that these containers support both iterators (begin, end) and reverse iterators (rbegin, rend). Well, ok, except forward_list, special alternative to list when reverse iteration not needed.
Now we will solve a simple task like iterating a QList backwards with a new means available (similar to this http://stackoverflow.com/questions/16441447/iterating-over-a-qlist-backwards):
#include <QCoreApplication>
#include <iostream>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QList<int> list = {1, 2, 3, 4};
QList<int>::const_reverse_iterator cIter;
cIter = list.crbegin();
while(cIter != list.crend()) {
std::cout << *cIter << std::endl;
++cIter;
}
return a.exec();
}
Output from this program is: 4 3 2 1
QList::crbegin() points to the first item in the list in the reverse order. It returns const_reverse_iterator.
QList::crend() points to the last item in the list in the reverse order. It also returns const_reverse_iterator.
reverse_iterators and const_reverse_iterators are working well with auto C++11 keyword. Here is the example:
#include <QCoreApplication>
#include <QVector>
#include <iostream>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QVector<int> qVector = {1, 2, 3, 4, 5};
for (auto it = qVector.rbegin(); it != qVector.rend(); ++it)
{
std::cout << *it << std::endl;
}
return a.exec();
}
As you may guess, the output from this simple program is: 5 4 3 2 1
