Difference between this->field and Class::field?

Question

I'm wondering something in C++.

Admitting the following code:

int bar;
class Foo
{
public:
    Foo();
private:
    int bar;
};

Inside my class, is there any difference between this->bar and Foo::bar? Are there cases where one is invalid?

Answer 1

Inside class Foo (specifically) there is no difference between the two given that bar is not static.

Foo::bar is called the fully qualified name of the member bar, and this form is useful in scenarios where there may be several types in the hierarchy defining a member with the same name. For example, you would need to write Foo::bar here:

class Foo
{
  public: Foo();
  protected: int bar;
};

class Baz : public Foo
{
  public: Baz();
  protected: int bar;

  void Test()
  {
      this->bar = 0; // Baz::bar
      Foo::bar = 0; // the only way to refer to Foo::bar
  }
};