stl container to store more than 1 type

**sujeet1** · 05-08-2007

Hi i got a design issue here.

I got

Code:

     class patient{
     }
  
    class dayPatient:public patient{
     }
    
     class outPatient:public patient{
     }
int main void(){
   // stl container
}

i need a stl container to store the day patients and outpatients.any type of container allows it? i tried vector,but vector allows only 1 type of patient.
Hope someone can tell me how to store both the daypatient and outpatient in a single stl container.

Thanx

**UMR_Student** · 05-08-2007

If your classes are polymorphic, you can do it like this:

Code:

patient* foo = new dayPatient;
patient* bar = new outPatient;
std::vector<patient*> patients;
patients.push_back(foo);
patients.push_back(bar);
//etc...

**ChaosEngine** · 05-08-2007

note that if you do it this way you should really wrap vector in a class so that patients are deleted in the destructor e.g.

Code:

class PatientColl
{
    std::vector<patient*> m_patients;

    static void DeletePatient(patient *pPatient)
    {
        delete pPatient;
    }
public:

    ~PatientColl()
    {
        for_each(m_patients.begin(), m_patients.end(), DeletePatient);
    }

    void AddPatient(patient *pPatient)
    {
        m_patients.push_back(pPatient);
    }
};

or you could save yourself the trouble and use a boost.PtrContainer which does this for you (see my sig)

**sujeet1** · 05-08-2007

hey umr student, thanx for your reply.my problem does get partly solved by using pointers.

Code:

class patient{
private:
public:
	void print(){
		cout<<"\nprint method from patient class ";
	}
};

class outPatient:public patient{
public:
	void print(){
		cout<<"\n OVER RIDED METHOD  ";
	}
	void print2(){
		cout<<"\nOUT newly defined print method ";
	}
};

int main(void){
	
	patient *a1=new patient;
	patient *b1=new outPatient;
	a1->print(); //works
	b1->print(); // doesn't output correctly.want it to output "OVER RIDED METHOD"
	//b1->print2(); // DOESNT compile
}

hope someone can help me out to get it to output the right data.

**prog-bman** · 05-08-2007

You need to declare your methods as virtual if you want the child class to override the parent class

Code:

#include <iostream>
#include <string>
using std::cout;
using std::string;
using std::endl;
using std::cin;

class CBaseClass
{
public:
	virtual string GetClassMessage()
	{
		return "I am the Base Class";
	}
};

class CChildClass : public CBaseClass
{
public:
	virtual string GetClassMessage()
	{
		return "I am the Child Class";
	}
};

int main()
{
	CBaseClass *ptrBase = new CBaseClass();
	CBaseClass *ptrChild = new CChildClass();


	cout<<"Base Message = "<<ptrBase->GetClassMessage()<<endl;
	cout<<"Child Message = "<<ptrChild->GetClassMessage()<<endl;

	cin.get();
}

**sujeet1** · 05-08-2007

thanx..i got 1 error rectified. but i still got one last wierd error left.

Code:

class CChildClass : public CBaseClass
{
public:
	virtual string GetClassMessage()
	{
		return "I am the Child Class";
	}
	
	string print()
	{
		return "HEY,HAVE A GOOD DAY";
	}
};

int main()
{
	CBaseClass *ptrBase = new CBaseClass();
	CBaseClass *ptrChild = new CChildClass();
	
	cout<<"Base Message = "<<ptrBase->GetClassMessage()<<endl;
	cout<<"Child Message = "<<ptrChild->GetClassMessage()<<endl;
	cout<<"Child Message = "<<ptrChild->print()<<endl;
}

i added the print method and tried to call.but it doesn't work? whats my mistake?

**prog-bman** · 05-08-2007

You can only call methods of the base class from that pointer, if you want to cast that pointer to the child you can then call the child methods.

Code:

#include <iostream>
#include <string>
using std::cout;
using std::string;
using std::endl;
using std::cin;

class CBaseClass
{
public:
	virtual string GetClassMessage()
	{
		return "I am the Base Class";
	}
};

class CChildClass : public CBaseClass
{
public:
	virtual string GetClassMessage()
	{
		return "I am the Child Class";
	}

	string Print()
	{
		return "Hey, Whats Up";
	}
};

int main()
{
	CBaseClass *ptrBase = new CBaseClass();
	CBaseClass *ptrChild = new CChildClass();


	cout<<"Base Message = "<<ptrBase->GetClassMessage()<<endl;
	cout<<"Child Message = "<<ptrChild->GetClassMessage()<<endl;

	CChildClass *ptrRealChild = reinterpret_cast<CChildClass*>(ptrChild);

	cout<<"Child Print Message = "<<ptrRealChild->Print()<<endl;

	cin.get();
}

**CornedBee** · 05-09-2007

Code:

CChildClass *ptrRealChild = reinterpret_cast<CChildClass*>(ptrChild);

Yikes! Absolutely not!!!

If you really, really, really, really, really have to cast a base to the child, you use a dynamic_cast. (And you check if the return value is NULL, because it will be if the object is not actually of the child type.)
But it would be far better to have a properly designed base class where the cast isn't necessary.

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