inheritance and namespaces

Question

I am trying a my first useful object oriented program with some namespace usage. I have a base class B which is in the namespace NS. If I try to inherit from this base class to get the inheritance work, I should use the NS::B in the class decleration as below, is this really the case? Or is there a more widely accepted sytle for this inheritance syntax?

namespace NS
{
    class D: public NS::B{
    ...
    };
}

Best, Umut

score 12 · Accepted Answer · answered Dec 01 '10 at 15:54

12

If your D is in namespace NS, you don't have to qualify NS::B, since D and B are in the same namespace. You can just use class D : public B.

answered Dec 01 '10 at 15:54

Eli Bendersky

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score 8 · Answer 2 · edited May 23 '17 at 12:01

8

When you are inside of namespace NS, you don't usually⁽¹⁾ need to qualify the names of functions, classes, or other entities that are in the namespace NS. Given:

namespace NS {
    class B { };
}

the following two definitions of D are the same:

namespace NS {
    class D : public NS::B { };
}

and:

namespace NS {
    class D : public B { };
}

(1) Argument-Dependent Lookup (ADL) can cause some ugly issues, especially when using templates, and to fix them you may need to qualify names.

edited May 23 '17 at 12:01

Community

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1

answered Dec 01 '10 at 15:54

James McNellis

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I guess I did a mistake somewhere in the makefile, this is what I would expect as well, thanks for the replies anyway. – Umut Tabak Dec 01 '10 at 15:56
@Umut: you can always try simple "what if" enquiries like this in a minimal single file. – Eli Bendersky Dec 01 '10 at 15:57
How did you add the raised footnote? – John Dibling Dec 01 '10 at 16:16

score 3 · Answer 3 · answered Dec 01 '10 at 15:59

You dont need to denote NS since you are already inside it

namespace NS
{
    class D: public B{ //is fine
    };
}

Something else you might find interesting later is :

#include <iostream>
int x = 10;

int main()
{
    int x = 5;
    //This will show the local x
    std::cout << x << std::endl;
    //This is how you access the Global x
    std::cout << ::x << std::endl;

    return 0;
}

inheritance and namespaces

3 Answers3