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

From: Daryle Walker (darylew_at_[hidden])
Date: 2008-08-20 17:37:15

On Aug 20, 2008, at 10:42 AM, Peter Barker wrote:

> 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_buffer.html#briefexample) 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 T, class Alloc>
> 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.

A forward declaration can provide defaults for template parameters.   
This is what is being done here, the main header is "boost/ 
circular_buffer.hpp" and its forward declaration, with default  
allocator, is at "boost/circular_buffer_fwd.hpp".

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT hotmail DOT com