C++ Inheritance operator<< - c++

Question

I have a few objects (classes) that all inherit from a base class Structure. These objects all print differently as they have different member variables but share common functions.
I want to be able to have a list of structures and print them without having to cast them back into their specific object, ie: Structure -> Building.
Is this possible in C++?
class Structure
{
};
class Building : public Structure
{
public:
friend std::ostream& operator<<(std::ostream& o, const Building &b)
{
return o << b.m_windows.size() << b.m_doors.size();
}
protected:
Windows m_windows;
Doors m_doors;
};
class Statue : public Structure
{
public:
friend std::ostream& operator<<(std::ostream& o, const Statue &s)
{
return o << s.m_type;
}
protected:
StatueType m_type;
};
int main(int argc, char* argv[])
{
Structure struct* = new Building();
std::cout << struct << std::endl;
return 0;
}
Error:
error: cannot bind 'std::ostream {aka std::basic_ostream<char>}' lvalue to 'std::basic_ostream<char>&&'
std::cout << struct << std::endl;
Edit:
I've isolated the issue in my own code, here is a compilable version (C11). The problem is that I am using further inheritance and the output of my command is:
CORRECT_VALUE<random address>
8.8.8.80x804c504
I'm not sure why it appends that random address?
http://pastebin.com/81ubU0yX

Answer 1

Create a virtual output function and call it within the operator <<. Override this output function in your derived classes.
class Structure
{
public:
virtual ~Structure() {}
virtual std::ostream& StreamOut(std::ostream& o) const { return o; }
friend std::ostream& operator<<(std::ostream& o, const Structure &s)
{
return s.StreamOut(o);
}
};
class Building : public Structure
{
public:
virtual std::ostream& StreamOut(std::ostream& o) const
{
return o << m_windows.size() << m_doors.size();
}
protected:
Windows m_windows;
Doors m_doors;
};
class Statue : public Structure
{
public:
virtual std::ostream& StreamOut(std::ostream& o) const
{
return o << m_type;
}
protected:
StatueType m_type;
};
int main(int argc, char* argv[])
{
std::unique_ptr<Structure> myStruct(new Building());
std::cout << *myStruct << std::endl;
}