What are qualified-id/name and unqualified-id/name?

Question

I was wondering if someone could explain there terms since I encounter them in many places. I know some basic theory about them but not sure what I know is right or wrong.

So can any one please explain these terms?

Answer 1

A qualified name is one that has some sort of indication of where it belongs, e.g. a class specification, namespace specification, etc. An unqualified name is one that isn't qualified.

Read James McNellis' answer here:

What is a nested name specifier?

Given:

struct  A {     struct B {         void F();     }; }; 

• A is an unqualified-id.
• ::A is a qualified-id but has no nested-name-specifier.
• A::B is a qualified-id and A:: is a nested-name-specifier.
• ::A::B is a qualified-id and A:: is a nested-name-specifier.
• A::B::F is a qualified-id and both B:: and A::B:: are nested-name-specifiers.
• ::A::B::F is a qualified-id and both B:: and A::B:: are nested-name-specifiers.

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Answer 2

A qualified name is one that specifies a scope.
Consider the following sample program, the references to cout and endl are qualified names:

#include <iostream>  int main()   {    std::cout<<"Hello world!"<<std::endl;    return 0; } 

Notice that the use of cout and endl began with std::. These make them Qualified names.

If we brought cout and endl into scope by a using declaration or directive*(such as using namespace std;), and used just cout and endl just by themselves , they would have been unqualified names, because they would lack the std::.