Question

I need a queue on n items where insertion of (n+1)^th item removes the 0^th item and insertion can only be made on the “back”.
Is there any such structure already there in boost or standard library?

Answer 1

You can use a boost::circular_buffer wrapped by a std::queue, something like this:

#include <queue>
#include <boost/circular_buffer.hpp>

typedef std::queue<my_type, boost::circular_buffer<my_type>> my_queue;
const int n = 3;
...
my_queue q(boost::circular_buffer<my_type>(n));
q.push(1);
q.push(2);
q.push(3);
q.push(4); // queue now contains 2,3,4