[Boost-users] Implementation question about boost::circular_buffer and allocator

Hello,   I've been going through the Boost libraries and encountered boost::circular_buffer. My question is not with the operation of Boost.Circular Buffer as-such, but about how the instantiation of it works without specifying the allocator.   The introductory example in the documentation(http://www.boost.org/doc/libs/1_35_0/libs/circular_buffer/doc/circular_buffe...) contains the following line:        // Create a circular buffer with a capacity for 3 integers.      boost::circular_buffer<int> cb(3);   But looking at the header file base.hpp in the circular_buffer directory, we have the following:   template class circular_buffer { ......   };   The Alloc template parameter is not a default one, so I can't understand how we can instantiate cb in the example?   Apologies if this is not strictly boost-user related.   Regards,   Jim