Question

Here is my code –

#include <iostream>
#include <conio.h>

using namespace std;

class Base
{
public:
int a;

};

//int Base::a = 5;

class Derived : public Base
{

public:
int static a;
};

int main()
{
   Derived d;
   cout<<d.a;
   getch();
   return 0;
}

I get a linker error here. But when I do it the other way round –

class Base
{
public:
int static a;

};

int Base::a = 5;

class Derived : public Base
{

public:
int a;
};

I get no error. Can someone please explain what is happening here.

Answer 1

All static members have to be explicitly defined/initialized outside the class.

In the second example you do this correctly (int Base::a=5), but in the first example you don’t do this for Derived::a, adding the following line to the first example should solve it:

int Derived::a = 5;