In C++, the scope resolution operator is ::. It is used for the following purposes.
1) To access a global variable when there is a local variable with same name:
// C++ program to show that we can access a global variable // using scope resolution operator :: when there is a local // variable with same name #include<iostream> using namespace std;
int x; // Global x
int main()
{ int x = 10; // Local x
cout << "Value of global x is " << ::x;
cout << "\nValue of local x is " << x;
return 0;
} |
Value of global x is 0 Value of local x is 10
2) To define a function outside a class.
// C++ program to show that scope resolution operator :: is // used to define a function outside a class #include <iostream> using namespace std;
class A {
public :
// Only declaration
void fun();
}; // Definition outside class using :: void A::fun() { cout << "fun() called" ; }
int main()
{ A a;
a.fun();
return 0;
} |
fun() called
3) To access a class’s static variables.
// C++ program to show that :: can be used to access static // members when there is a local variable with same name #include<iostream> using namespace std;
class Test
{ static int x;
public :
static int y;
// Local parameter 'x' hides class member
// 'x', but we can access it using ::
void func( int x)
{
// We can access class's static variable
// even if there is a local variable
cout << "Value of static x is " << Test::x;
cout << "\nValue of local x is " << x;
}
}; // In C++, static members must be explicitly defined // like this int Test::x = 1;
int Test::y = 2;
int main()
{ Test obj;
int x = 3 ;
obj.func(x);
cout << "\nTest::y = " << Test::y;
return 0;
} |
Value of static x is 1 Value of local x is 3 Test::y = 2
4) In case of multiple Inheritance: If the same variable name exists in two ancestor classes, we can use scope resolution operator to distinguish.
// Use of scope resolution operator in multiple inheritance. #include<iostream> using namespace std;
class A
{ protected :
int x;
public :
A() { x = 10; }
}; class B
{ protected :
int x;
public :
B() { x = 20; }
}; class C: public A, public B
{ public :
void fun()
{ cout << "A's x is " << A::x;
cout << "\nB's x is " << B::x;
} }; int main()
{ C c;
c.fun();
return 0;
} |
A's x is 10 B's x is 20
5) For namespace If a class having the same name exists inside two namespaces we can use the namespace name with the scope resolution operator to refer that class without any conflicts
#include <bits/stdc++.h> #include <iostream> using namespace std;
#define nline "\n" // Global Declarations string name1 = "GFG" ;
string favlang = "python" ;
string companyName = "GFG_2.0" ;
// You can also do the same thing in classes as we did in // our struct example class Developer {
public :
string name = "krishna" ;
string favLang = "c++" ;
string company = "GFG" ;
// Accessing Global Declarations
Developer(string favlang, string company)
: favLang(favlang)
, company(companyName)
{
}
}; int main()
{ Developer obj = Developer( "python" , "GFG" );
cout << "favourite Language : " << obj.favLang << endl;
cout << "company Name : " << obj.company << nline;
} |
favourite Language : python company Name : GFG_2.0
6) Refer to a class inside another class: If a class exists inside another class we can use the nesting class to refer the nested class using the scope resolution operator
// Use of scope resolution class inside another class. #include <iostream> using namespace std;
class outside {
public :
int x;
class inside {
public :
int x;
static int y;
int foo();
};
}; int outside::inside::y = 5;
int main()
{ outside A;
outside::inside B;
} |