[Boost-users] boost::bind upgrading from 1.33.1 to 1.34.1 problem

5 Dec 2007

      Hello,

I'm upgrading from boost 1.33.1 to 1.34.1 and upgrade does not let me
compile the following code:

// CRefCounted provides functionality to CRefPtr to have
// referenced pointers
struct CNode: public CRefCounted
{
	void GetName(){}
};

int main(int argc, char **argv){
	typedef CRefPtr<CNode>	CPNode;
	typedef std::multimap<std::string, CPNode> TPNodes;
	TPNodes Children;
	std::for_each(
		Children.begin(),
		Children.end(),
		boost::bind(
			&CNode::GetName,
// problem in the next line
			boost::bind(&TPNodes::value_type::second,_1)));
	return 0;
}

I get the following messages from MSVC8.0:
error C2784: 'T *boost::get_pointer(const boost::shared_ptr<T> &)' :
could not deduce template argument for 'const boost::shared_ptr<T> &'
from 'const CPNode'
error C2784: 'T *boost::get_pointer(const std::auto_ptr<_Ty> &)' : could
not deduce template argument for 'const std::auto_ptr<_Ty> &' from
'const CPNode'
error C2784: 'T *boost::get_pointer(T *)' : could not deduce template
argument for 'T *' from 'const CPNode'

If I replace CRefPtr with boost::shared_ptr the code compiles. Hence I
assume the problem is with the way I implemented CRefPtr class. Here it is:
template<typename T> class CRefPtr {
private:
	T* m_ptr;
public:
	CRefPtr(T* ptr=NULL)
		:m_ptr(NULL){
		*this=ptr;
	}
	CRefPtr(const CRefPtr<T>& ptr)
		:m_ptr(NULL){
		*this=ptr;
	}
	~CRefPtr() {
		if (m_ptr) {
			m_ptr->DecrementReference();
			m_ptr=NULL;
		}
	}
	CRefPtr<T>& operator=(T* ptr) {
		if(ptr!=m_ptr) {
			if(m_ptr) {
				m_ptr->DecrementReference();
			}
			m_ptr=ptr;
			if(m_ptr) {
				m_ptr->IncrementReference();
			}
		}
		return *this;
	}
	CRefPtr<T>& operator=(const CRefPtr<T>& ptr){*this=ptr.m_ptr;return *this;}
	T* operator->() const{return m_ptr;}
	T& operator*() const{return *m_ptr;}
	bool operator<(const CRefPtr<T>&
obj)const{if(obj.m_ptr<this->m_ptr)return true;else return false;}
	T* get() const{return m_ptr;}
	operator T*()const{return m_ptr;}
};

What am I missing?

Some explanation on why I went this route. I am using CRefPtr instead of
shared_ptr because full CNode class has a member CNode* m_Parent. I
could not figure out how to use weak pointers, but if I use CRefPtr I
can assign a simple pointer returned by GetParent() to a CPNode and it
would still work, while I could not achieve this result with shared_ptr.
Maybe someone can direct me to a place which explains how to handle such
situations properly with shared_ptr.

Thanks.

-- 
Regards, Alexander.           http://sjcomp.com

[Boost-users] boost::bind upgrading from 1.33.1 to 1.34.1 problem

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