Question

I’m writing a custom circular buffer implementation with fixed capacity (fixed at runtime by call to constructor, no resize methods) and want it to be STL-compatible.
My goal is to make it a Random Access Container. Additionally I want it to have the specific interface of an Back Insertion Sequence, but without being a sequence (no resize and inserting/erasing at arbitrary positions, …). So it would only be an extended Random Access Container.
After reading some questions about max_size() and size(), I’m still a little confused.

My current idea:
size(): number of elements contained in buffer
max_size(): capacity of buffer (maximum number of elements it can hold)

Is this correct (conforming to standard / STL)? Or do I have to handle it like (std::)array with size() == max_size()?

Answer 1

The standard is quite clear on the meaning of max_size() in C++11 Table 96:

distance(begin(), end()) for the largest possible container

If, like std::array, the size is a property of the container type (e.g. specified by a template parameter), then that should be the same as size(). If you can instantiate the same type with various sizes, then it should be the largest allowed size.

I would follow the example of the standard containers, and have a capacity() function to tell you the capacity.