What data structure discards the oldest item when a new one is added?

Question

I've been trying to remember this and it's driving me crazy.

Basically, it's like a small array, of let's say size five, and as you add items it starts to fill up. When it's full, and you add a new item, the oldest one (first added) is removed.

You can access the values by something like variable[0], variable[1] etc, where variable [0] is the oldest value, and variable 4 the newest.

Any ideas on what this is called? Is it a standard C++ type, or did I just see it somewhere as a custom class?

Answer 1

Boost Circular Buffer

http://www.boost.org/doc/libs/1_46_1/libs/circular_buffer/doc/circular_buffer.html

From the Boost docs:

  // Create a circular buffer with a capacity for 3 integers.
  boost::circular_buffer<int> cb(3);

  // Insert some elements into the buffer.
  cb.push_back(1);
  cb.push_back(2);
  cb.push_back(3);

  int a = cb[0];  // a == 1
  int b = cb[1];  // b == 2
  int c = cb[2];  // c == 3

  // The buffer is full now, pushing subsequent
  // elements will overwrite the front-most elements.

  cb.push_back(4);  // Overwrite 1 with 4.
  cb.push_back(5);  // Overwrite 2 with 5.

  // The buffer now contains 3, 4 and 5.

  a = cb[0];  // a == 3
  b = cb[1];  // b == 4
  c = cb[2];  // c == 5