Re: smart pointers
On 14 Feb, 13:57, Cholo Lennon <chololen...@hotmail.com> wrote:
On Feb 14, 10:27 am, ke...@bytebrothers.co.uk wrote:
When I am using the private implementation idiom, is there anything to
be gained by using a boost::scoped_ptr as opposed to a auto_ptr? I
confess I'm not that clear on the differences...
If your classes are noncopyable: a const auto_ptr to hold the pimpl is
almost the same than scoped_ptr: scoped_ptr can be 'reset' to change
the pointee pimpl. You can't change the pointee pimpl with const
auto_ptr
If your classes are copyable: auto_ptr can't be const and non const
auto_ptr leads you to the disaster due to auto_ptr's transfer
ownership. When my classes are copyable I prefer using shared_ptr to
hold the pimpl (to avoid the manual coding of pimpl copy)
I'm unclear exactly what non-copyable means in this context. The
following seems to copy just fine.
Here's part of a wrapper class for an MD5 hash I've been playing with
to get to grips with this pimpl stuff:
//-----------------------------------
#include <boost/scoped_ptr.hpp>
#include <stdint.h>
#include "hash.h"
class MD5Private;
class MD5 : public virtual Hash
{
public:
using Hash::hash;
using Hash::end;
using Hash::digest;
MD5();
MD5(const MD5& h);
MD5& operator= (const MD5& h) throw();
virtual ~MD5() throw();
virtual void begin () throw();
virtual void hash (const uint8_t* data, const uint_32t& len)
throw();
virtual void end (const uint8_t* hval) throw();
private:
boost::scoped_ptr<MD5Private> p_;
};
//--------------------------
and in the relevant bits of the class definition I currently have:
//--------------------------
class MD5Private {
public:
uint32_t i[2];
uint32_t buf[4];
uint8_t in[64];
uint8_t digest[16];
};
// New object, so initialise
MD5::MD5() : p_(new MD5Private()) { begin(); }
// Copy object, so do _not_ initialise
MD5::MD5(const MD5& other) :
Hash(other),
p_(other.p_.get() ? new MD5Private(*other.p_) : NULL)
{ }
MD5::~MD5() throw() { }
MD5&
MD5::operator= (const MD5& rhs) throw()
{
MD5 temp(rhs);
swap(p_, temp.p_);
return *this;
}
//<etc, etc>
//--------------------------
Are you saying that by using a boost::scoped_ptr this should not work?