cpp library

[hellcoder]

i want to know that #include <iostream> it included std. input output library and
using namespace std also included standard lib. then why we have to write both things? please explain it in detail!

[Dy7SLyTq]

because the std namespace is spread across the whole stl

[hellcoder]

actually i am beginner would you mind to please explain it in detail i didn't get your last reply!

[Dy7SLyTq]

iostream didnt include std. it gives the user the abiltity to bring anything contained in the std namespace (in that file at least) into scope with the command using.

[hellcoder]

got it! thank you very much!

[hellcoder]

one more thing i wanna ask that is iostream is a subset of using namespace std?

[Dy7SLyTq]

no its a header that has all of its code contained in std

[Disch]

hellcoder:

You seem to be confusing headers and namespaces.

Including a header gains you access to any objects/functions/classes/etc that are defined in that header. For example, when you #include <iostream> , you gain access to std::cout, std::cin, std::ostream, etc, etc.


Notice how all of that has the 'std::' prefix. That is because it is all defined within the std namespace:

// a fully functional example program
#include <iostream> // for std::cout, std::endl

int main()
{
    std::cout << "hello world" << std::endl;
    return 0;
}

What using namespace std; does... is it takes everything in the std namespace and dumps it into the global namespace (effectively destroying the entire point of having a separate namespace).

This lets you access objects without the std:: prefix (ie.. you can just type cout instead of std::cout) but increases the likelihood of name conflicts in your program... since you might accidentally name a function/class the same thing as something already in the std namespace.

[hellcoder]

ohh..thats the thing! thank you very much disch!..:) keep it up! carry on helping beginners like me!