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CppScopeOperator

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(C++) Scope operator ::

The operator to get into a scope, being the double colons ::. This scope can be in a namespace or a class.

Function namespace

Here is a code snippet showing how to have the same functions in two different namespaces and how to call them:

include <iostream>


namespace myFirstNamespace
{
  void sayHello()
  {
    std::cout << "Hello from myFirstNamespace" << std::endl;
  }
}
namespace mySecondNamespace
{
  void sayHello()
  {
    std::cout << "Hello from mySecondNamespace" << std::endl;
  }
}
int main()
{
  std::cout << "Hello from main" << std::endl;
  myFirstNamespace::sayHello();
  mySecondNamespace::sayHello();
}

Class namespace

include <iostream>


class MyClass
{
  public:
  static void sayHello() { std::cout << "Hello world" << std::endl; }
};
int main()
{
  MyClass::sayHello();
}

The sayHello static member function is a bit of a trivial example (Click here for a better example). More often you use the scope operator when having a derived class calling functions explicitly from its base class:

struct MyBaseClass
{
  virtual void sayHello() const 
  { 
    std::cout << "Hello MyBaseClass" << std::endl; 
  }
};
struct MyDerivedClass : public MyBaseClass
{
  void sayHello() const 
  { 
    std::cout << "Hello MyDerivedClass" << std::endl; 
  }
  void lie() const 
  { 
    MyBaseClass::sayHello(); 
  }
};

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