namespace

This is a discussion on namespace within the C++ Programming forums, part of the General Programming Boards category; We import namespace into scope by "using" keyword. Is it possible to kick it out of scope?...

  1. #1
    System Novice siavoshkc's Avatar
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    namespace

    We import namespace into scope by "using" keyword. Is it possible to kick it out of scope?
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  2. #2
    Its hard... But im here swgh's Avatar
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    Im not sure, but try looking at the header library files with your compiler. If you can understand what they mean, try impementing a function that might do the opposite. Of course, a compiler has loads of header files with it, but try namespace.h or even winproc.h.

  3. #3
    The larch
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    Something like that?

    Code:
    #include <iostream>
    
    namespace John {
        void Message()
        {
            std::cout << "John's message!" << std::endl;
        }
    }
    
    namespace Mary {
        void Message()
        {
            std::cout << "Mary's message!" << std::endl;
        }
    }
    
    using John::Message; //global namespace
    int main()
    {
        
        Message();  //John::
        { 
            using Mary::Message; //in this scope
            Message(); //Mary::
        }
        Message();  //John::
        std::cin.get();
    }
    Actually just typing std:: (or any other namespace identifier) each time where needed quickly becomes a second nature. And it makes code clearer.

  4. #4
    System Novice siavoshkc's Avatar
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    Something like this
    Code:
    using namespace std;
    //code 
    unuse namespace std;
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  5. #5
    (?<!re)tired Mario F.'s Avatar
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    I don't think it is possible. A namespace is essentially the introduction of a scope. The using directive (using namespace foo) brings the whole of that scope into view. Only by leaving the scope at which the using directive was used will you essentially remove access to it.

    The same happens to the using declaration (using foo:bar). It brings a name into view at the current scope. You will need to leave that scope to remove that name from view.

    Creating nested scopes will not help because, as you probably already know, scopes carry on downwards.
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  6. #6
    The larch
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    You should just start typing std::cout, std::cin, std::string etc. If you are writing your own header files, you are strongly discouraged to use global using after all. And it's not as inconvenient as it may seem.

    Then you won't have problems that you might have.

  7. #7
    System Novice siavoshkc's Avatar
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    You should just start typing std::cout, std::cin, std::string etc. If you are writing your own header files, you are strongly discouraged to use global using after all.
    It is exactly what I want to escape from and reason of this thread:-).
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  8. #8
    The larch
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    Escaping good practices tends to lead to problems

    If you have some identifiers that are conflicting with things in std namespace, you could put them in a separate namespace and use them with the namespace identifier (e.g my::cout) when they are needed.

    Code:
    #include <iostream>
    using namespace std;
    
    namespace my {
        int cout;
    }
        
    int main()
    {
        
        my::cout = 5;
        cout << my::cout << endl;
        cin.get();
    }
    Or just avoid conflicting names?

  9. #9
    System Novice siavoshkc's Avatar
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    It is just a technical question. I don't have a real world problem.
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  10. #10
    The superhaterodyne twomers's Avatar
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    I think he wants it so that he can use a namespace in one place (like a header), then unuse it so it doesn't affect whatever program he's writing; where he may be using another namespace.

    I've no idea I'm afraid.

  11. #11
    System Novice siavoshkc's Avatar
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    I need a new keyword: "dontuse"
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  12. #12
    (?<!re)tired Mario F.'s Avatar
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    Other than introducing scopes into the code there is no other way.

    Code:
    int main() {
    
        int a = 12;
        
        std::cout << a << '\n'; // Ok
        
        {
            using namespace std;
            cout << a << '\n'; // Ok
        }
        
        cout << a << '\n'; \\ Error!
    
    }
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  13. #13
    The superhaterodyne twomers's Avatar
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    I reckon the only way to unuse is to not use...

  14. #14
    Code Goddess Prelude's Avatar
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    >It is just a technical question. I don't have a real world problem.
    Namespaces aren't like macros. If you use them correctly, the hypothetical problem you're talking about simply doesn't exist.
    My best code is written with the delete key.

  15. #15
    Registered User whiteflags's Avatar
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    Explicit scoping, just do it.
    Code:
    #include <iostream>
    
    namespace Mary {
      void message() { std::cout << "Mary says hello.\n"; }
    }
    
    namespace John {
      void message() { std::cout << "John says hello.\n"; }
    }
    
    namespace Walter {
      void message() { std::cout << "Walter says hello.\n"; }
    }
    
    int main()
    {
      Walter::message();
      John::message();
      Mary::message();
    }
    Lame.

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