classes and objects

I have done this :

Code:

---

#include<iostream>
#include<string>

class student
{
        private:
       
        int score;
        string surname;
       
        public:
       
        student(string asurname, int ascore);
        ~student();
        string getSurname();
        int getScore();
};
        student::student(string asurname, int ascore)
        {
                surname = asurname;
                score = ascore;
        }
       
        student::~student()
        {
        }
       
        string student::getSurname()
        {
                return surname;
        }
       
        int student::getScore()
        {
                return score;
        }


using namespace std;


int main()
{
        student Mike("Senikoglou", 20);
        cout << Mike.getSurname();
        cout << Mike.getScore();
       
        return 0;
}

---

having the class and the main fuction on the same cpp file, but how can I use 2 different files one for the class and one for the tester file(the main)???

Put the class declaration in a header file, and the class definition in a .cpp file which #includes the header file.
In the .cpp with the main(), #include the header file.

Code:

---

#include<iostream>
#include<string>

class student
{
        private:
       
        int score;
        string surname;
       
        public:
       
        student(string asurname, int ascore);
        ~student();
        string getSurname();
        int getScore();
};

---

Code:

---

#include<string>
#include<student.h>

        student::student(string asurname, int ascore)
        {
                surname = asurname;
                score = ascore;
        }
       
        student::~student()
        {
        }
       
        string student::getSurname()
        {
                return surname;
        }
       
        int student::getScore()
        {
                return score;
        }

---

Code:

---

#include<iostream>
#include<string>
#include<student.h>

using namespace std;
/*student::student(string surname, int score);
int student::getScore();
string student::getSurname();*/

int main()
{
        student Mike("Senikoglou", 20);
        Mike.getSurname();
        Mike.getScore();
       
        return 0;
}

---

I am having the following question. Do I have to declare the fuctions of my class in the main.cpp??? If yes how??? If I run with comments(it compiles) I get :


[Error] C:\ undefined reference to `student::student(basic_string<char, string_char_traits<char>, __default_alloc_template<0, 0> >, int)'
[Error] C:\: undefined reference to `student::~student(void)'
[Error] C:\ undefined reference to `student::getSurname(void)'
[Error] C:\: undefined reference to `student::getScore(void)'
[Error] C:\: undefined reference to `student::~student(void)'

--------------------without comments:-----------------

[Error] C:\ declaration of `student::student(basic_string<char,string_char_tr aits<char>,__default_alloc_template<false,0> >, int)' outside of class is not definition
[Error] C:: declaration of `int student::getScore()' outside of class is not definition
[Error] C:\: declaration of `class string student::getSurname()' outside of class is not definition

No, you declare them in the header.
I noticed you use string a lot in the header & .cpp files. Since you didn't put using namespace std; in the header (and you should NEVER EVER do that anyways) the compiler should be saying it doesn't know what string is.
Change string to std::string in all places, since it's in the std namespace.

BTW, what compiler are you using?
If it's VC++, make sure all files are part of the Project.
If you're using a makefile, make sure you're compiling both .cpp files and linking them both into the final executable.

I added using namespace in all of the 3 files. I still get ERROR 1 mentioned above

Both cpp files have to be compiled and linked together. Are both added to your project/makefile/command line?

Also, #include<student.h> should be #include "student.h". Use quotes for your own headers and brackets for library headers.

Finally, don't forget to add header include guards to your header file. It probably doesn't matter here, but it might cause you a problem soon.

Quote:

---

Originally Posted by mixalissen

I added using namespace in all of the 3 files.

---

That's exactly what I said not to do.
Read this: Chapter 59. Don't write namespace usings in a header file or before an #include

Well I found the solution. I need only 2 files instead of 3; thanx for the help; class deglaration and definition should be together...It seems that I misunderstood one of your suggestions...

>> class deglaration and definition should be together...

No, that's wrong. It might work in this simple example, but that is not the "proper" way to divide the code up and will cause you problems in bigger projects.

Code:

---

#include<string>
#include<student.h>
class student
{
        public:
        student(int asurname, int ascore)
        {
                surname = asurname;
                score = ascore;
        }
       
        student::~student()
        {
        }
       
        string student::getSurname()
        {
                return surname;
        }
       
        int student::getScore()
        {
                return score;
        }
};

---

Code:

---

#include<iostream>
#include<string>

using namespace std;

class student
{
        private:
       
        int score;
        int surname;
       
        public:
        student(int surname, int score);
        ~student();
        int getSurname();
        int getScore();
};

---

Code:

---

#include<iostream>
#include<string>
#include"student.h"

using namespace std;

int main()
{
        student Mike(23, 20);
        cout << Mike.getSurname();
        cout << Mike.getScore();
       
        return 0;
}

---

That's what I have so far. But I get " redefinition of class student" when I compile the first class. How is this solved???

Go back to the code in post #3. That was correct after you made the std namespace change. The current code is not really close because you are defining the class twice.

Then fix the project or makefile or command line to compile and link the files properly. As cpjust asked, what compiler/IDE are you using. That knowledge will help us help you solve the problem.

C-free 4

ps: still undefined reference

what about linking??? fixing project ??? etc if you can pls be more specific I am new to this

I fixed it, oh god it time to sleep.... Thanx a lot guys been helpful...

I'm not familiar with C-free 4, so I cannot give advice on how to use it properly. You have to find out how to tell it that you have two source files and that both need to be compiled and linked together. Are both the source files named with a cpp file extension?

Is there a reason you are using that IDE instead of more common and free alternatives (like VC++ Express, Code::Blocks or Dev-C++)?

Actually I did not solve anything....F#$ck. All this time I have a file student.cpp that contained both declaration and definition of the class so main saw the fuctions from there and not fom the 2 latest
files with seperate def and declar. I think that the answer will be in linking the files but I do not know how to do this. Anyway its getting late. I hope I get some answers tommorow...Thanx for your time guys...

I was posting while you were posting... I have dev c++ yes both are cpp. How can I go about linking them with dev c++?

Well, to be honest I haven't used dev-c++ in a long time myself, but there are many people here who have who will hopefully chime in. I think you have to add the two cpp files to a project, then build the project.

I haven't really used Dev-c++, but VS Express will handle all these details for you. It might be good for you since you don't seem to understand the process.
What you typically do is just add all your .cpp files to your project and then just build and everything is done for you.

I believe I did it... Well I thought so yesterday too, but I was wrong...

the code in post 3 has the correct division of definition and implementation files, just link them properly.

Quote:

---

Originally Posted by cpjust

No, you declare them in the header.
I noticed you use string a lot in the header & .cpp files. Since you didn't put using namespace std; in the header (and you should NEVER EVER do that anyways) the compiler should be saying it doesn't know what string is.
Change string to std::string in all places, since it's in the std namespace.

BTW, what compiler are you using?
If it's VC++, make sure all files are part of the Project.
If you're using a makefile, make sure you're compiling both .cpp files and linking them both into the final executable.

---

On what arguments one should never use ' using namespace std; ' ? One argument to use it is that for VisualStudio6, and yes old compilers are still in use, some stuff had been declared in the global namespace.
So with explicitely specifying the namespace with the scope operator, this can cause errors.

I've only seen that in regards to C library names (e.g. rand(), strcmp, printf, etc) on VC++ 6.0. Explicitly stating the namespace works on that compiler on C++ library names (e.g. string, cout, vector, etc).

Besides, you really shouldn't worry about appeasing VC++ 6.0 in your current code. That compiler is too old to pay attention to.

My rule on using namespace std is to never use it and always use std::. The general rule is that you should never put a using namespace directive before other code that is included. That means don't put it in a header, because once the compiler sees it in your header it will do it for all source files that include that header and all other header files included after that header. Also you shouldn't put it before other headers in a source file for the same reason. I prefer not to have to remember all that and just use std:: everywhere.

Quote:

---

Originally Posted by MarkZWEERS

On what arguments one should never use ' using namespace std; ' ? One argument to use it is that for VisualStudio6, and yes old compilers are still in use, some stuff had been declared in the global namespace.
So with explicitely specifying the namespace with the scope operator, this can cause errors.

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Did you click on that link and read Chapter 59?