relationship between std and iostream

[sawer]

this is code:

#include <iostream>
 using namespace std;
int main()
{   
	cout<<"Hello world";
	return 0;
}

here i must write both #include <iostream> and using namespace std; i don't understand why such a expression we need.Where is cout?Is it in iostream or std?

Also said that iostream library is part of std.So why do we write include file.Also if std cover iostream why don't we write first
using namespace std;
then #include <iostream>
I don't understand relationship between two expression.
Any help will be greatly appreciated

[hk_mp5kpdw]

foo.h

#ifndef FOO_H
#define FOO_H

namespace foo
{
    int bar;
}

#endif

foo.cpp

#include "foo.h"
using foo::bar;
int main()
{
    bar = 5;
    return 0;
}

As an example, the integer variable bar is declared within the foo namespace in the foo.h header file which is #included in our foo.cpp source file. Understand this and then apply it to the std namespace/iostream header problem you are having.

The headers are usually needed to provide the basic declaration of objects and their interface (the member functions) and data members and their types. A lot of this is done for type-checking purposes by the compiler. The actual code for the functions are typically contained within "libraries".

[sawer]

ok.thanks.
Can we say every standart library include namespace std so std covers every std library.I mean
string.h
[code]
namespace std
{
//memebers
}
[/]code
or
iostream.h

namespace foo
{
   //members.
}

like these...

[Daved]

Basically yes, every C++ standard header has its contents placed within the std namespace.

However, string.h is a standard C header that is standard in C++ but has a preferred C++ version: <cstring>. So <string.h> does not have its contents in the std namespace, but its C++ counterpart <cstring> does.

Also, iostream.h is not standard at all. So if you have an old compiler that supports <iostream.h>, then it will not have its contents in the std namespace. However, the new, correct and standard version, <iostream>, does have its contents in the std namespace.

So just replace the old headers in your example with the new, standard C++ headers and it will be correct.

[sawer]

ok.thank you.
I understand what you mean.

Good works...