c++ 공부를 시작했는데 namespace 공부를 하다가 막혔습니다. ㅠㅠ 궁금한 점에 대해서 구글링 하던중, 답은 못찾았고 저랑 정확하게 같은 궁금증을 가진 분이 올린 질문을 찾았습니다. 다음은 그 질문을 편집한 것입니다.

Say for example there are 100 name definitions in the namespace std, if I were to include all of them using the "using" declaration (Option1), it still would not be the same as "using" directive (Option2)

Option1 - using declaration Code: using std::cout; using std::cin; .... //Assume I mention all the rest of the name definition in std using std::

Option2 - using directive Code: using namespace std; Now option1 and option2 (assuming they are specified in the same point in the code) aren't the same, I would like to know how / why they are different.

assuming there are 2 namesaces "Hello" and "GoodBye" and both have a function message().

Test1 - Following is legal: Code:

using namespace Hello; using namespace GoodBye; the above would present a problem ONLY when the function message() is called.

Test2 - Following is illegal: Code: using Hello::message; using GoodBye:: message;

this is probably the proof that using "using directive" is not same as multiple application of "using delcaration"s.

결국 질문은 using 지시자가 왜 using 선언을 여러번 적용한 것이랑 다른지, 어떻게 다른지 입니다.