unresolved overloaded function type

问题

I'm trying to write a templated class that holds a reference to an object of it's template parameter type, and a pointer to a void returning no arg member function of that class. However I'm getting an error about '<unresolved function type>' when I compile.

template<class T>
class memberAction
{
public:
    memberAction(void (T::*func)() , T& object);
private:
    void (T::*m_func)();
    T& m_object;
};

template<class T>
memberAction<T>::memberAction(void (T::*func)() , T& object)
{
    m_func = func;
    m_object = object;
}

class File
{
public:
    File();
    void TELUNUS_Open();

    //memberAction<File>& getOpenAction();

private:
    memberAction<File> m_OpenAction;
};

File::File():
        m_OpenAction(TELUNUS_Open,*this)//Line with error on it
{

}

void File::Open()
{ 
    //
}

compiling with g++ 4.7.2 I get the following error message:

StackOverloadErrorExample.cpp|31|error: no matching function for call to 'memberAction<File>::memberAction(<unresolved overloaded function type>, File&)'|

It seems other people with a similar compiler error are confusing pointers to global functions with pointers to member functions, but I specifically declare the constructor as taking a pointer to a member function of it's template parameter, and pass it a member function of the correct type.

So how do I resolve this compiler error?

回答1:

I believe you need to pass &File::TELUNUS_Open—or &File::Open, whichever name you’ve actually called it—to get the member function pointer. Open has the function type void (File::)() whereas &File::Open has the type you really want, the function pointer type void (File::*)(). Beyond that, you’re going to have issues with the m_object reference member. The assignment operator will try to assign to an uninitialised reference:

template<class T>
memberAction<T>::memberAction(void (T::*func)() , T& object)
{
    m_func = func;
    m_object = object;
}

You should use a constructor initializer list instead:

template<class T>
memberAction<T>::memberAction(void (T::*func)() , T& object)
  : m_func(func),
    m_object(object) {}

回答2:

This compiles, I believe:

template< class T >
class memberAction
{
 public:
  memberAction( void (T::*)(), T& );
 private:
  void (T::*m_func)();
  T& m_object;
};

template< class T >
memberAction< T >::memberAction( void (T::*func)(), T& object )
    : m_func( func ), m_object( object )
{    
}

class File
{
 public:
  File();
  void TELUNUS_Open()
  {
   return;
  }

  //memberAction<File>& getOpenAction();

 private:
  memberAction< File > m_OpenAction;
};

File::File()
    : m_OpenAction( &File::TELUNUS_Open, *this ) //Line with error on it
{
}

来源：https://stackoverflow.com/questions/15845230/unresolved-overloaded-function-type

标签

c++

templates

g++

function-pointers