c++ - How to enforce parent / derived relationship of two independent classes inside a container? -

consider following class definitions:

#include <string>  class cparty { public:     cparty();     virtual ~cparty();     int m_nid; };  class cpartyex : public cparty { public:     cpartyex();     ~cpartyex();     std::string m_sname; };  class ctransaction { public:     ctransaction();     virtual ~ctransaction();     int m_nclassno; };  class ctransactionex : public ctransaction { public:     ctransactionex();     ~ctransactionex();     std::string m_sdesc; };  class cobject { public:     cobject();     ~cobject();     cparty* m_pparent;     ctransaction* m_ptransaction; }; 

in appropriate implementation, create following types of cobject storage objects:

// ok: basic party basic transaction cobject iobject1; iobject1.m_pparent = new cparty(); iobject1.m_ptransaction = new ctransaction();  // ok: extended party extended transaction cobject iobject2; iobject2.m_pparent = new cpartyex(); iobject2.m_ptransaction = new ctransactionex(); 

however, current cobject definition not prevent mixing cparty , ctransaction types incompatible 1 another:

// not intended: basic party extended transaction cobject iobject3; iobject3.m_pparent = new cparty(); iobject3.m_ptransaction = new ctransactionex();  // not intended: extended party basic transaction cobject iobject4; iobject4.m_pparent = new cpartyex(); iobject4.m_ptransaction = new ctransaction(); 

is somehow possible place restriction on how 2 objects can linked inside cobject instance?

you encapsulate decision in cobject constructor:

class cobject { public:     cobject(bool extended = false); };  cobject::cobject (bool extended) {     if (extended)     {         m_pparent = new cpartyex();         m_ptransaction = new ctransactionex();     }     else     {         m_pparent = new cparty();         m_ptransaction = new ctransaction();     } }