Newbie Question

[slx47]

my compiler adds this automatically:

using namespace std;

what is it and what does it do ?

[CornedBee]

namespaces are a C++ feature that allows you to group variables and functions together, but not as closely as they are in classes.
A namespace is simply that: a space in which names exist:

namespace myspace
{
  int i;
  float f;
}

i = 4;  // doesn't work! wrong scope
myspace::i = 3;  // does work, scope resolution operator

This allows you to avoid conflicts of global variables (very useful when you work on a team).

namespace a
{
 int somevar;
}

namespace b
{
  int somevar;
}

somevar = 3;  // which one?

a::somevar = 5;  // this is unambigous
b::somevar = 9;

By convention, all functions/classes/variabels in the C++ runtime library are grouped together in the large namespace std.
Because writing std::... every time may be annoying, there is the using keyword. You can use it to import certain identifiers or a whole namespace to global scope.

#include <iostream>

using std::cout; // import cout to global scope

cout << "Hello";  // now possible
cout << endl;  // not possible, endl is not imported

using namespace std;  // import the whole std namespace to global scope

int i;
cin >> i;
cout << i << endl; // possible, all symbols imported

I hope that clears it up some.

[abdul]

Originally posted by CornedBee
namespaces are a C++ feature that allows you to group variables and functions together, but not as closely as they are in classes.
A namespace is simply that: a space in which names exist:
[code]
namespace myspace
{
int i;
float f;
}

Just curious, what if declared a variable called "i" outside the namespace myspace? I hope it won't give you any error and will let you use that ouside i.

[nabeels786]

you can still use it

if you had

int i;

void blah(){

     int i;

}

you can access the global i like

::i