Circular Buffer

Hi /prog/

Some time ago I started to write a well designed library of useful algorithms in C. As long as I needed more stuff, I simply added pieces.

Today I'm pretty bored, so I'd like to add an implementation for circular buffers. Since however I don't really need it (it's just for fun), I'm wondering which is the most useful semantics for a circular buffer.

For instance:
[list]
[*] Is it worthy to write a primitive which applies a function on every availabe element from the oldest to the most recent?
[*] What if the buffer is full and I want to insert a new element? Should I overwrite the oldest one or should I make the request fail instead?
[/list]

Which are, in general, the kind of functionalities you'll prefer?

>>13
Sorry, should be:

for (size_t i = 0, end = cbuffer_size(cb); i < end; ++i) {
   void *value = cbuffer_at(cb, i);
   // do something with value
}