Namespaces in C++
Namespaces allow to group entities like classes, objects and functions under a name. This way the global scope can be divided in “sub-scopes”, each one with its own name.
The format of namespaces is:
namespace identifier
{
entities
}
Where identifier is any valid identifier and entities is the set of classes, objects and functions that are included within the namespace. For example:
namespace myNewNamespace
{
int a;
}
The keyword using is used to introduce a name from a namespace into the current declarative region.
Example
// using namespace example
#include <iostream>
using namespace std;
namespace first
{
int x = 5;
}
namespace second
{
double x = 3.1416;
}
int main()
{
{
using namespace first;
cout << x << endl;
}
{
using namespace second;
cout << x << endl;
}
getchar();
return 0;
}
Output
5 3.1416
In our program whereas we use cout, cin we used std::cout and std::cin, this is also way to access namesapces, and we can also do it by using keywork like this :
Example
#include <iostream>
using namespace std; // system namespace
int main()
{
cout << "hello using namespace";
getchar();
return 0;
}
Output
hello using namespace
