error: expected primary-expression before '.' token

Honourable Mist · #1 18-Feb-2006, 04:57

Could someone tell me what the error message "error: expected primary-expression before '.' token" means, or at least what I'm doing wrong?
Here's the code:

CPP / C++ / C Code:

//main.cpp
#include <cstdlib>
#include <iostream>
#include <time.h>
#include <fstream>

#include "algorithms.cpp"
#include "board.cpp"
#include "database.cpp"

using namespace std;

int main()
{
    database.createSessionfile(); // error goes here
    return (0);
}

CPP / C++ / C Code:

//database.cpp
#include <fstream>
#include <time.h>
#include "database.h"

using namespace std;

int database::createSessionfile()
{
 long name = time(NULL);
 ofstream sessionfile;
 sessionfile.open((const char*)name);
 sessionfile << name << '\n';
}

CPP / C++ / C Code:

//database.h
using namespace std;

class database {
      public:
             int createSessionfile();
};

Some irrelevant code such as other functions in class database have been omitted.

Also: hi, everyone!

Paramesh · #2 18-Feb-2006, 07:45

Hi Mist,

Welcome to the GID Forums.

The problem is that you have not created an instance of the class, or to be simple, you have not created a variable of the type database.

Class can be simply defined as a user defined datatype, for example, similar to string.
How do you declare a string?
string str;
Then you can access the string functions such as length etc isnt it?

Similarly, create a new variable of type database like this:
database db;
Then, you can access the member function like this:
db.createSessionfile();

Also instead of [code] and [/code] you can use [c++] and [/c++] tags.

Regards,

Paramesh.

Honourable Mist · #3 18-Feb-2006, 09:25

Oh, it's so obvious now that you mention it! Thanks for the quick reply aswell!

I have probably made some equally silly mistake, for now I'm getting multiple definition errors for every single function. The only change is in main.cpp:

CPP / C++ / C Code:

#include <cstdlib>
#include <iostream>
#include <time.h>
#include <fstream>

#include "algorithms.cpp"
#include "board.cpp"
#include "database.cpp"

using namespace std;

obj_database database; //renamed the class database to obj_database

int main()
{
    database.createSessionfile();
    return (0);
}

5had0w · #4 18-Feb-2006, 09:42

Hey! I know this is off topic but everytime i see one of your posts with C/C++ code, I see you always use

CPP / C++ / C Code:


using namespace std;

What is this for?

Thanks in advance,

5had0w

Paramesh · #5 18-Feb-2006, 09:46

Quote:

Originally Posted by Honourable Mist

Oh, it's so obvious now that you mention it! Thanks for the quick reply aswell!

I have probably made some equally silly mistake, for now I'm getting multiple definition errors for every single function. The only change is in main.cpp:

CPP / C++ / C Code:

#include <cstdlib>
#include <iostream>
#include <time.h>
#include <fstream>

#include "algorithms.cpp"
#include "board.cpp"
#include "database.cpp"

using namespace std;

obj_database database; //renamed the class database to obj_database

int main()
{
    database.createSessionfile();
    return (0);
}

Add the header files to the code, rather than the cpp files..

Multiple definition errors are caused due to multiple inclusion of the header files.

For example, consider that your class is in database.h
You create another file algorithm.h where you include the database.h file.
Again in your main.cpp file, you include both database.h and algorithm.h.

What happens now?
You include the file database.h two times!!!

How to avoid this problem?
Use conditional compile statements #ifndef, #define and #endif.
For example, you can do like this:

CPP / C++ / C Code:

#ifndef _DATABASE_
#define _DATABASE_

// class definition here...

#endif

in every header file.

Now what happens?
The first time you try to include the database.h file, _DATABASE_ is not defined. So it is defined now, and the class definition is included.
The next time you try to include the database.h file, _DATABASE_ is already defined, and the code is not included.
This prevents redefinition errors.

Hope i explained it clear.
Regards,

Paramesh.

Paramesh · #6 18-Feb-2006, 09:52

Quote:

Originally Posted by 5had0w

Hey! I know this is off topic but everytime i see one of your posts with C/C++ code, I see you always use

CPP / C++ / C Code:


using namespace std;

What is this for?

Thanks in advance,

5had0w

Namespaces are new concepts in C++, which is used to avoid name conflicts, for example, two classes with same name..

You can find more information here:
Namespaces

Inside the namespace std, there are various classes, and members.
For example, cin, cout, endl are inside the namespace std;
In order to use them, you should specify in which namespace they are present.
Either you can write like this:
using namespace std;
and use cin or cout, etc.

Or you could prefix the namespace with scope resolution operator like this:

CPP / C++ / C Code:


std::cout<<"Cout is in namespace std"<<std::endl;

Regards,

Paramesh.

5had0w · #7 18-Feb-2006, 10:02

Thanks!
I've been always using since I started programming this way:

CPP / C++ / C Code:


cout << "Hi! How are you?" << endl;

and it works but I think I need to change...

Thanks again!

Cumps

Paramesh · #8 18-Feb-2006, 10:12

Quote:

Originally Posted by 5had0w

Thanks!
I've been always using since I started programming this way:

CPP / C++ / C Code:


cout << "Hi! How are you?" << endl;

and it works but I think I need to change...

Thanks again!

Cumps

That is because you must've included: iostream.h

But the standards have changed, and you should only use:
#include<iostream>
(This file defines the std namespace.)

and NOT like this:
#include<iostream.h>
The last one is deprecated, and is not defined inside a namespace.

Regards,

Paramesh.

5had0w · #9 18-Feb-2006, 10:18

Oh ok! Thanks dude

And sorry for off topic.

Cumps

Honourable Mist · #10 18-Feb-2006, 11:51

Quote:

Add the header files to the code, rather than the cpp files..

I'm not sure what you mean.

Quote:

Multiple definition errors are caused due to multiple inclusion of the header files.

For example, consider that your class is in database.h
You create another file algorithm.h where you include the database.h file.
Again in your main.cpp file, you include both database.h and algorithm.h.

What happens now?
You include the file database.h two times!!!

I was actually really careful about only including files once

Quote:

How to avoid this problem?
Use conditional compile statements #ifndef, #define and #endif.
For example, you can do like this:

CPP / C++ / C Code:

#ifndef _DATABASE_
#define _DATABASE_

// class definition here...

#endif

in every header file.

Now what happens?
The first time you try to include the database.h file, _DATABASE_ is not defined. So it is defined now, and the class definition is included.
The next time you try to include the database.h file, _DATABASE_ is already defined, and the code is not included.
This prevents redefinition errors.

I did this with all my headers, but the problem remains! I even tried doing the same thing with the cpp-files aswell, but no change.

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error: expected primary-expression before '.' token

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