What does the "::" mean in C++?

Question

What does this symbol mean?

AirlineTicket::AirlineTicket() 

Answer 1

:: is the scope resolution operator - used to qualify names. In this case it is used to separate the class AirlineTicket from the constructor AirlineTicket(), forming the qualified name AirlineTicket::AirlineTicket()

You use this whenever you need to be explicit with regards to what you're referring to. Some samples:

namespace foo {   class bar; } class bar; using namespace foo; 

Now you have to use the scope resolution operator to refer to a specific bar.

::foo::bar is a fully qualified name.

::bar is another fully qualified name. (:: first means "global namespace")

struct Base {     void foo(); }; struct Derived : Base {     void foo();     void bar() {        Derived::foo();        Base::foo();     } }; 

This uses scope resolution to select specific versions of foo.

Answer 2

In C++ the :: is called the Scope Resolution Operator. It makes it clear to which namespace or class a symbol belongs.