namespace example

// https://www.geeksforgeeks.org/namespace-in-c/

#include <iostream>
using namespace std;

// first name space
namespace first_space {
   void func() {
      cout << "Inside first_space" << endl;
   }
}

// second name space
namespace second_space {
   void func() {
      cout << "Inside second_space" << endl;
   }
}

using namespace first_space;
//using namespace second_space;

int main () {
   // This calls function from first name space.
   func();
 
   return 0;
}





http://www.cplusplus.com/doc/tutorial/namespaces/

using

The keyword using introduces a name into the current declarative region (such as a block), thus avoiding the need to qualify the name. For example:

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// using #include <iostream> using namespace std; namespace first { int x = 5; int y = 10; } namespace second { double x = 3.1416; double y = 2.7183; } int main () { using first::x; using second::y; cout << x << '\n'; cout << y << '\n'; cout << first::y << '\n'; cout << second::x << '\n'; return 0; }