Thread: C++ cout

namespaces are useful if you make a function library. Their purpose is to reduce name clashes. Also it helps a human reader understand what a function or variable is for if they are grouped together under a common name. i.e all graphics functions could be grouped under a gfx namespace...

Code:

namespace gfx {
    void Initialize();
    void Render();
    void Shutdown;
}

Instead of

Code:

    void gfx_Initialize();
    void gfx_Render();
    void gfx_Shutdown();

Of course you wouldn't make the gfx scope globle because Initialize, Shutdown and Render are popular names for functions. So you would use the scope operator.

Code:

gfx::Initialize();

When calling a function.

Namespaces are open, i.e.

Code:

namespace bob {
    int x, y;
}

namespace bob {
    std::string name;
}

namespace bob {
    int age;
}

You can keep adding names whenever you want.

could just include stdafx.h and never have to type std:: ever

Code:

#include <iostream>

int main()
{

      cout <<"Hello World!\n";

return 0;
}

it works for me

You dont need namespace someone should of just told him this in the first place

Devil Panther,

Ignore the comment about :: for now. CornedBee was talking about the first :: in ::std::cout. You cannot ignore the middle :: in std::cout.

The std namespace is used by all standard library headers in C++. This includes <iostream>, <fstream>, <string>, <vector>, <cstdlib>, <cstdio>, <cmath>, and many others. To use the things from those headers, you have to tell the compiler that the thing you are using is from the std namespace. There are different ways of doing this.

One is to tell the compiler to always check the std namespace for any name you use (this is the using namespace std; option).

Another is to tell the compiler that any time you use a specific name, to check the std namespace (this is the using std::cout; option).

Another is to tell the compiler every single time that the name you are using is from the std namespace (this is the std::cout option).

There are different ways to use those options as well. The point is that standard library names live in the std namespace, and if you want to use one of them you have to tell the compiler to look there for them.

example 1

Code:

using namespace std;     // pull in everyting from namespace std
cout << i << endl;       // no std:: needed because compiler looks for everything in namespace std
cin >> i;                // like above

example 2

Code:

using std::cout;          // pull in only cout from namespace std
cout << i << std::endl;   // no std:: needed for cout because compiler looks for cout
std::cin >> i;            // std:: is needed because compiler looks only for cout

example3

Code:

                               // no using declaration
std::cout << i << std::endl;   // std:: needed because nothing is pulled in 
std::cin >> i;                 // like above

Kurt

3) Ignore the ::std::cout. Basically there is a global namespace that you access with the first ::, but rarely do you need to worry about it.

2) Yes. In C++, all standard library headers put all the names into the std namespace. There are lots of standard library headers besides the examples I gave.

1) Here are examples of the three options I mentioned:

Code:

#include <iostream>
using namespace std;

int main()
{
    cout << "Hello World" << endl;
    return 0;
}

Code:

#include <iostream>
using std::cout;
using std::endl;

int main()
{
    cout << "Hello World" << endl;
    return 0;
}

Code:

#include <iostream>

int main()
{
    std::cout << "Hello World" << std::endl;
    return 0;
}

Did you read the FAQ on namespaces? Did you understand CornedBee's explanation of a namespace above? std is just a namespace. The people who standardized the language decided to put the standard library stuff into a namespace, and they decided to call it std (for standard).

You'll have to do some reading elsewhere if the explanations in this thread aren't enough to explain namespaces.

std is the standard functions.

Let me simplify even further - and use VB to explain.

In VB, I might have a function that is native to the language such as Open for opening files for read/write. In VB, if I type in Open, open, OPEN, OpEn, or any combination of cased letters, the VB IDE would correct the case to Open and now that it's a restricted keyword. In debugging a VB application, if I try to step into the line that says Open, I don't see anything. The Open word doesn't take me to a deeper level.

C++ is case sensitive. Restricted keywords are not auto-corrected for case. IF and if are viewed as two different objects, the first being some sort of variable and the latter is part of an if/then statement. If I am stepping through a C++ program and come upon specific "keywords," the debugger will take me to definitions of those words in their original header files. (note, I might be a bit off in my description but conceptually it should be close.)

std is a huge namespace of common functions/processes typically used in a c++ program. HOWEVER, the "power" of c++ is the compiler only grabs what is absolutely necessary to run the program. VB, on the otherhand, says grab anything that COULD be needed.