<iostream.h> or <iostream>?

Here is a simple code:

Code:

---

        // abc.cpp
        # include<iostream.h>
          void main()
          {
            int a=1,b=2,c;
            c=a+b;
            cout<<"c="<<c<<endl;
          }

---

in VC++6, it passed compling and linking all right. If use <iostream> to replace <iostream.h>, the vc6 prompts:

error C2065: 'cout' : undeclared identifier
error C2065: 'endl' : undeclared identifier

BUT in VC7, use <iostream.h>, it says:

fatal error cannot open include file 'iostream.h': no such file or directory.

If changed to <iostream>, it says:

Error c2065: 'cout': undeclared identifier.
Error c2065: 'endl': undeclared identifier.

What is the reason? How deal with?

the problem is namespacing

The simplest solution is to add "using namespace std" after "#include <iostream>"

Another bad thing is your use of void main, main should have type int

EDIT
Here is you code, nicely formatted and working

Code:

---

// abc.cpp
# include<iostream>
using namespace std;
int main()
{
    int a=1,b=2,c;
    c=a+b;
    cout<<"c="<<c<<endl;
}

---

<iostream> (as well as all the conventional C++ libraries) is defined under the std namespace. Either use the appropriate using namespace line at the top of your program:

Code:

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#include <iostream>

using namespace std;

---

or preceed all functions and identifiers from those libraries with its namespace.

Code:

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std::cout << std::endl;

---

It's apparent that you are a beginner, so for now don't worry about what everything means, and just use this template for all your programs:

Code:

---

#include <iostream>
using namespace std;

int main()
{
 
    //your code here

    return 0;

}

---

Depending on what compiler you are using, you may need to add:

Code:

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cin.get();

---

before the line:

Code:

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return 0;

---

to keep the console window open so that you can see the output from your program.

Or use iostream.h to know whats going on.

» Or use iostream.h to know whats going on.
What do you mean by that?

Just

Code:

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#include<iostream.h>

---

And no need to specify a namespace. If it compiles then it's OK.

No it's not.

Don't post like that if so, i will answer: IT IS!

And I will answer: <iostream.h> is a non-standard header in C++, so don't use it. Period. And if it compiles okay, throw out your compiler and get a new one.

I don't know a single modern C++ compiler that won't compile <iostream.h>.

They'll all give a warning though. It's a bad habit to use antiquated headers, as they might lose their functionality in the future. This is why you use <iostream>.

Hmm, you're right. Well then, if it doesn't give a warning... ;)

>>And if it compiles okay, throw out your compiler and get a new one.
Then we should throw out the microsoft!!!

Quote:

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Then we should throw out the microsoft!!!

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No, you should throw out Microsoft Visual C++ 6. If you insist on using a Microsoft compiler, the one from Visual C++ 2005 Express should be fine, especially since the package is available as a free download till November this year, or something like that, and you can continue using it for free even after that.

The cost of the IDE is not a problem for me (look where am i). But I don't have any problem with my compiler, I like it! I think it is not a problem for a compiler to compile a code, the problem is when it doesn't.

Quote:

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But I don't have any problem with my compiler, I like it! I think it is not a problem for a compiler to compile a code, the problem is when it doesn't.

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The problem is that your current compiler is outdated and thus not standards compliant. So yes, you will find that your compiler will be unable to compile standards compliant code in some cases, especially if they use advanced constructs not previously widely supported.

EDIT:
Well, I took a look at the features listed in MS Visual C++ 2005, and on the "Powerful Language and Libraries" page there is the claim:
"Earlier versions of Visual C++ didn’t support the advanced C++ features required to successfully compile some of these libraries. Now, with Visual C++ 2005’s improved ISO compliance, it is very easy to incorporate code from these libraries."

The library examples being Loki, Boost, Blitz and Crypto++, boost in particular being very useful.

<iostream.h> is provided by most compilers for backwards compatibility only. As far as I'm aware it's basically the same as <iostream> but without the namespace support.
Similar for the others.

It's not recommended to be used in new code of course.

>> I don't know a single modern C++ compiler that won't compile <iostream.h>
The OP already indicated that VC++ 7 (2003) won't compile <iostream.h>. It doesn't even give you a helpful error message.

>> If it compiles then it's OK.
You made the decision to use the old headers because it works on your compiler. That doesn't mean it is the proper decision to advise other programmers to follow. Many people here cannot help you because they use VC++ 2003 or 2005 and your examples don't compile. It is a very simple change to use the correct headers, even in VC++ 6, and so not doing so just gives the impression that you would prefer to save yourself a single line of typing over making it easier on those who are trying to help you. Besides, purposefully choosing the old way that is no longer being supported when you can use the new way right now without changing your compiler is the type of decision that leads towards a poor career as a programmer.

Actually I use old headers because I don't know what "name space" exactly is. And I wont use what I don't know. But finally I'll learn it (i hope), and will use it.

Namespaces.

Tnx SirCorno6
If iostream.h is an iostream without namespace why a new compiler can't compile it?
Even if iostream.h is older it is in standard c++ , shouldn't it compile?

Lol, theyse programming holy wars happen all to often :).

Just use the basic <iostream> using namespace std; Otherwise your compiler will probably get mad :p.

>> If iostream.h is an iostream without namespace why a new compiler can't compile it?

That's not necessarily true. Some compilers will do that for iostream (like VC++ 6), but there are often differences between the standard iostream stuff and what each compiler vendor used to do in their version of iostream.h.

>>you would prefer to save yourself a single line of typing over making it easier on those who are trying to help you.

Why? I only used old iostream.h anybody can change it to iostream (press backspace twice) and add "using namespace std;" it should not bother anybody, does it? If I used another old header, please inform me.

Is this true that iostream and iostream.h both use stdio?
If no, why stdio.h is included in them?
I took a look into both iostream and iostream.h. They were completely different (in design)and iostream.h was more understandable, stdio.h was included in both(not in the file itself but in one of deeper included headers). They each use their own headers (ex. ios vs ios.h), but there was also useoldio.h in iostream.h. That file force code to use classic iostream libraries.

> I took a look into both iostream and iostream.h. They were completely different (in
> design)and iostream.h was more understandable, stdio.h was included in both
Yeah, and so every other compiler will be the same right?
Not a chance matey.

Get used to the namespace version would be my suggestion, it's the way the future is going so you may as well get used to it at the outset.

Anything else is just the "turboC on XP defence"

I saw laserlight's link, MVC2005 is like an icecream, I'll get it soon.

I'm pretty new to c++ but I can't see why people always say to go for 'using namespace std'. I prefer to put a 'using std::cout' instead (or using std::<iostream function call here>). Just dumping the whole std namespace into all of your files just cuts down the function names you can use, plus if you have a wierd function in the file it's far easier to see that it's from 'std::' if you have it explicitly at the top of your file.

I wouldn't care, but I get the impression that people say to just go for 'using namespace std' because they somehow think that it makes it easier that way... Whether it does or doesn't, IMHO it's one of the easiest bits of the language to learn so why not start off right?

That's a genuine question. People here don't just dump the std namespace do they?

No. In this case, I think many are saying that it isn't hard to move from <iostream.h> to <iostream>, the least you have to do is add the "using namespace std;".

However, I personally, use std:: unless I am modifying code that does it a different way (which never happens except when answering questions on forums like this). I just prefer to be consistent, and there are other situations where adding the using directive is somewhat more dangerous (e.g. inside header files). So why not just use the same thing everywhere?

Another common usage is to put the using directive only inside the block of code that needs it. For example, you could put it inside main() at the very top.

Quote:

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People here don't just dump the std namespace do they?

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I think the general rule of thumb is to fully qualify identifier names in header files, and then to use the using declarations for the specific identifiers you want to use in source files.

Quote:

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Originally Posted by Daved

Another common usage is to put the using directive only inside the block of code that needs it. For example, you could put it inside main() at the very top.

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good idea. never thought of that myself to be honest. that way the namespace goes out of scope when the function does (this wouldn't be beneficial in main(), but could be in other functions).

I saw many tutorials that begin teaching with "using namespace std;" outside the main(), now I see this method is not so good. It makes a bad habit.