Using namespace std? [closed]

Question

I included the line using namespace std;on top of my code. Now consider the declaration int a,b,c;.Is above code an equivalent to int std::a,std::b,std::c;? If so, consider the following example:

If I declared(defined) a namespace Hi after the line using namespace std;. Is Hi a part of std i.e .., am I supposed to use Hi as std::Hi?

I'm a beginner .

Answer 1

Is above code an equivalent to int std::a,std::b,std::c;

No. A using namespace statement means that your code can use members of that namespace without having to qualify them with the namespace's name.

For example, say you have a #include <string> statement followed by a using namespace std; statement. You can then refer to the std::string class as just string instead.

Or, say you have a #include <iostream> statement followed by a using namespace std; statement. You can then refer to the std::cin and std::cout objects as just cin and cout, respectively.

Simply using a namespace does not add anything to that namespace. It is a way of bringing content from the specified namespace into the calling namespace.

If I declared(defined) a namespace Hi after the line using namespace std;. Is Hi a part of std

No. To do that, Hi would have to be declared inside of a namespace std block, eg:

namespace std {
    namespace Hi {
        ...
    }
}

But, that is undefined behavior (except in special cases), as you are generally not allowed to add things to the std namespace.