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Thinking in C++ Vol 2 - Practical Programming
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Iterators in reversible containers

A container may also be reversible, which means that it can produce iterators that move backward from the end, as well as iterators that move forward from the beginning. All standard containers support such bidirectional iteration.

A reversible container has the member functions rbegin( ) (to produce a reverse_iterator selecting the end) and rend( ) (to produce a reverse_iterator indicating one past the beginning ). If the container is const, rbegin( ) and rend( ) will produce const_reverse_iterators.

The following example uses vector but will work with all containers that support iteration:

//: C07:Reversible.cpp
// Using reversible containers.
#include <fstream>
#include <iostream>
#include <string>
#include <vector>
#include "../require.h"
using namespace std;
int main() {
ifstream in("Reversible.cpp");
assure(in, "Reversible.cpp");
string line;
vector<string> lines;
while(getline(in, line))
for(vector<string>::reverse_iterator r = lines.rbegin();
r != lines.rend(); r++)
cout << *r << endl;
} ///:~

You move backward through the container using the same syntax as you do when moving forward through a container with an ordinary iterator.

Thinking in C++ Vol 2 - Practical Programming
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire