Re: Using a std::vector as a variable-length receive buffer

In article <1186936026.342913.89050@k79g2000hse.googlegroups.com>,
  irotas <google@irotas.net> wrote:


I don't particularly like your solution... It creates a bunch of objects
that may or may not ever get used. I would do something more like this:

This is a stripped down version of a class that I use when I need an
array of objects that are not copy constructible or assignable.

    template< typename T >
class Buffer {
    T* begin;
    T* end;
    T* cap;
public:
    Buffer(): begin( 0 ), end( 0 ), cap( 0 ) { }

    /**
     * reinitializes elements (0, s].
     * postcondition: size() == s && capacity() >= s
     */
    void resize( size_t s ) {
       reserve( s );
       end = begin + s;
       for ( T* inc = begin; inc != end; ++inc )
          inc = new ( inc ) T;
    }

    /**
     * invalidates all elements.
     * postcondition: size() == 0 && capacity() >= s
     */
    void reserve( size_t s ) {
       for ( T* inc = begin; inc != end; ++inc )
          inc->~T();
       end = begin;
       if ( s > capacity() ) {
          ::operator delete( begin );
          begin = (T*)::operator new( s * sizeof( T ) );
          end = begin;
          cap = begin + s;
       }
    }

    T& operator[]( size_t i ) {
       assert( i < size() );
       return begin[i];
    }

    const T& operator[]( size_t i ) const {
       assert( i < size() );
       return begin[i];
    }

    size_t size() const {
       return end - begin;
    }

    size_t capacity() const {
       return cap - begin;
    }
};

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