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#2
October 19th, 2002, 09:20 PM
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Explained as simply as possible, namespaces allows us to group a set of global classes, objects and/or functions under a name. If you specify using namespace std then you don't have to put std:: throughout your code. The program will know to look in the std library to find the object. Namespace std contains all the classes, objects and functions of the standard C++ library.
Without namespace Code:
#include <iostream>
int main () {
std::cout << "Hello world!\n";
return 0;
}
With namespace Code:
#include <iostream>
using namespace std;
int main () {
cout << "Hello world!\n";
return 0;
}
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#3
October 19th, 2002, 11:26 PM
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yea and if you wanted, you could also create your own namespaces like so..
Code:
#include <iostream>
using namespace std;
namespace mystuff{
int value = 5;
}
int main()
{
cout << mystuff::value; //outputs 5
return 0;
}
or we could have. Code:
#include <iostream>
using namespace std;
namespace mystuff{
int value = 5;
}
using namespace mystuff;
int main()
{
cout << value; //outputs 5
return 0;
}
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#4
October 20th, 2002, 10:35 AM
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The whole idea of namespaces was to define a new level of scope. Sometimes different libraries and include files (especially from different third party vendors) have the same global variable or function names. For example, a socket library might define a global variable called max_connections to indicate max socket connections allowed. A database library may declare a global variable with the same name to indicate max connections to a database. This causes problems when a programmer wishes to use both libraries in a program. The concept of namespaces was put forward to solve this problem explicitly. The idea goes like this:
Code:
Code from library 1:
namespace YoyodyneSockLib {
int max_connections;
int get_connected_state();
int sock_func();
....
};
Code from library 2:
namespace FoobarDBLib {
int max_connections;
int get_connected_state();
int db_func();
....
};
Programmer's code:
#include "yoyodynesocklib"
#include "foobardblib"
using namespace YoyodyneSockLib;
using namespace FoobarDBLib;
...
...
x = db_func();
y = FoobarDBLib::get_connected_state();
...
...
cout << "max sock connections " << YoyodyneSockLib::max_connections << "\n";
cout << "max database connections " << FoobarDBLib::max_connections << "\n";
As you can see from the above code, namespaces were explicitly used to resolve the problem of conflicting function or variable names between the two libraries.
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