Answer Posted / rdl
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 myNamespace
{
int a, b;
}
In this case, the variables a and b are normal variables
declared within a namespace called myNamespace. In order
to access these variables from outside the myNamespace
namespace we have to use the scope operator ::. For
example, to access the previous variables from outside
myNamespace we can write:
myNamespace::a
myNamespace::b
The functionality of namespaces is especially useful in the
case that there is a possibility that a global object or
function uses the same identifier as another one, causing
redefinition errors. For example:
// namespaces
#include <iostream>
using namespace std;
namespace first
{
int var = 5;
}
namespace second
{
double var = 3.1416;
}
int main () {
cout << first::var << endl;
cout << second::var << endl;
return 0;
}
5
3.1416
In this case, there are two global variables with the same
name: var. One is defined within the namespace first
and the other one in second. No redefinition errors happen
thanks to namespaces.
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