newbie : compiling a C++ program in linux

Hi !

I recently shifted to linux OS and compilation of all my C programs on it has worked fine with the gcc compiler. I tried to compile my c++ programs on linux but it somehow gave me some errors which I cannot understand. I used the command
"g++ filename.cpp"

This is a simple program I tried to compile

Code:

---

#include<iostream>
int main()
{
        cout << " hello";
        return 0;
}

---

The error I get is :

Quote:

---

eg325.cpp: In function `int main()':
eg325.cpp:4: `cout' undeclared (first use this function)
eg325.cpp:4: (Each undeclared identifier is reported only once for each
function it appears in.)

---

what am I doing worng,

also when i replace the iostream with iostream.h why do I get a huge warning ?

Quote:

---

/usr/include/c++/3.2.2/backward/backward_warning.h:32:2: warning: #warning This
file includes at least one deprecated or antiquated header. Please consider using one of the 32 headers found in section 17.4.1.2 of the C++ standard. Examples
include substituting the <X> header for the <X.h> header for C++ includes, or <sstream> instead of the deprecated header <strstream.h>. To disable this warning
use -Wno-deprecated.

---

add "using namespace std;" just under your last include or swap 'std::cout' for 'cout'.

The .h versions of the C++ headers are, as the warning tells you, for backward compatibilty only and should never be used for new development.

You get an error because you havent told the compiler that cout is located in the standard namespace. There are 3 ways to fix this:

Code:

---

// For the lazy person but also least prefered method
#include <iostream>
using namespace std;
...

// A better method
#include <iostream>
using std::cout;

// The method that is considered best:
#include <iostream>
...
std::cout << "bla bla bla";

---

You get the warning because iostream.h is not a standard header and should not be used.

If you put
using std::cout;
You can only use the cout function of namespace std, correct?
So then you would need to put
using std::cin; also if you wanted to use cin.

I understand why you may not want to put using namespace std but why would this

Quote:

---

Originally Posted by Shakti

// The method that is considered best:
#include <iostream>
...
std::cout << "bla bla bla";

---

be better than this

Quote:

---

Originally Posted by Shakti

// A better method
#include <iostream>
using std::cout;

---

Ganoosh, yes, that's correct.

MadCow257, later, when you try to use the same technique when using sort() or max() or some other commonly named function, and it conflicts with one of your functions or another function in a library you are using, you will need to explicitly state the namespace that you are using. For cout, it is not a big deal, because few people use the "cout" name in their program.

BTW, another common technique is to put the using declaration or using directive inside the scope that you need it. So instead of making it global for the whole file, you just use it for the function or code block you need it for.