Having problems using multiple files

Hi, I'm workin on using a header file with 2 .cpp files to find the volume of a cylinder. Heres what I have for the header file.

Code:

---

class cylinder

{

        private:
                double r,l,v;

        public:
                double cylvol();
                          cylinder();
                void get_data();
};

---

the name for the header file is cylinder.cpp
::this is cylinder.cpp::

Code:

---

#include "cylinder.h"
#include <iostream>

using namespace std;

void cylinder::get_data()

{
        cout << "Please enter the radius and length of the Cylinder" << endl;
        cin >> r >> l;

        return;
};

double cylinder::cylvol()

{
        const double PI = 3.14157;
        v=PI*r*r*l;
       
        return v;
};

cylinder::cylinder()

{
        r = 0.0;
        l = 0.0;
        v = 0.0;
};

---

and last but not least the main program called foo.cpp

Code:

---

#include "cylinder.cpp"

int main()

{
        cylinder junk;

        junk.get_data();
       
        cout << "The volume of the cylinder is: " << junk.cylvol() << endl;

        return 0;
};

---

I get 3 link errors, please tell me what I'm doing wrong

In your main file replace #include "cylinder.cpp" with #include "cylinder.h" and add cylinder.cpp to your project.

You include the header in your main program not the cpp file

Hey thanks guys, figured it out already though. Had to change that one source file to a header file. Hey by the way can you have more than one source file like how I have it in this program?

What 3 linker errors? What compiler are you using?

Header files should generally not contain code (unless this is some templated code). You also should not be including one source file from another source file. Both cylinder.cpp and foo.cpp should include cylinder.h but that is it. The compiler then compiles the two source files into object files, cylinder.obj and foo.obj (for example). Then the linker combines the object files along with code from its libraries to produce the executable.

How you do the compiling and linking of a multifile program depends on the compiler you are using. If using an IDE of some kind this usually involves setting up a project and adding all your source files to the project and then hitting the "build" button. If using a command-line compiler/linker, then you need to specify all the source files you are using when you do the compilation/linking steps, the exact syntax of which will depend on your compiler/linker.

Mess around with the #ifndef and #endif preprocessor directives. This will allow better header inclusions because it will prevent recursive inclusion problems. There were some topics about this on this BBS, do a search for them :)

Most compilers I've seen allow multiple .cpp files, I don't know of anything current that doesn't. You might want to also check your compiler documentation for the specifics.

As Tronic said, you should look at the preprocessor statements. You will get linker errors if you two cpp files use the same include file, so to make sure that the include file only gets declared once, change your .h file to this:

Code:

---

#ifndef __CYLINDER_H //if something is not already defined as __CYLINDER_H
#define __CYLINDER_H //then define it and allow the following code
class cylinder

{

        private:
                double r,l,v;

        public:
                double cylvol();
                          cylinder();
                void get_data();
};
#endif

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