c++ - using std namespace and dependancies

Question

While trying to familiarize myself with c++ and its concepts, I came across the

using namespace std

and

#include <iostream>

my simple code is as follows

#include "stdafx.h"
#include "ConsoleApplication5.h"
#include <iostream>     

int main()
{
    std::cout << "hi";
    return 0;
}

Using Visual Studio 2015 Community, which uses intellisense, shows

cout

uses the following

std::ostream std::cout

As a C# programmer, this confuses me slightly. Is this :

std::ostream

being a return type while

std::cout

being the method/parameter passed or is

std::ostream

a dependancy of

cout

UPDATE (after Archimaredes Answer)

In C#, one can use the following:

StreamWriter srWrite;

or

StreamWriter srWrite = new StreamWriter(string filepath)

or one can use:

StreamWriter srWrite = new StreamWriter(new NetworkStream(Socket.GetStream()));

Each case a object of type namely

StreamWriter

is assignable with a new object or a existing file or a networkstream.

I tried the same after that which you mentioned (excuse the C# mentality) with the std::ostream x = new std:ostream which returns a no default constructor.

Could you just add how std::ostream and std::cout relate to each other, which creates/initalizes the other. THis concept is still a bit vague to me.

Answer 1

std::cout is an object in global scope, of type std::ostream. When you call std::cout << "hi", you are invoking the operator<<() method with the std::cout object as your left-hand value and the string literal "hi" as the right-hand value.

cout and ostream are inside the std namespace, hence the std:: prefix. If you place using namespace std in your code, this allows you to omit the prefixes, e.g.

#include <iostream>
using namespace std;

int main() {
    cout << "hi"; // no error because the 'std' is unnecessary now
}

Namespaces are used to prevent name conflicts, in exactly the same way as C#; it is usually good practice to not use using namespace directives for entire source code files in order to prevent name conflicts in your code.

---

Edit in response to OP's update

std::cout is an instance of std::ostream. To illustrate this, consider the following:

class A_Class {
public:
    A_Class() {}
    void foo() {}
};

int main() {
    A_Class an_instance;
    an_instance.foo();
}

A_Class is a class, while an_instance is an instance of A_Class.

Similarly; ostream is a class, while cout is an instance of ostream.

---

Edit in response to OP's comments

This may look confusing to a user of C#, but it is the exact same concept as:

int n = 5;

Whereint is the type, and n is the variable name.