Newbie Question

my compiler adds this automatically:

using namespace std;

what is it and what does it do ?

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;
}

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

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

Code:

---

namespace a
{
 int somevar;
}

namespace b
{
  int somevar;
}

somevar = 3;  // which one?

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

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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.

Code:

---

#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

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I hope that clears it up some.

Quote:

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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.

you can still use it

if you had

Code:

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int i;

void blah(){

    int i;

}

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you can access the global i like

Code:

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::i

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