Problems Compiling in a Project

[vettejeep]

I am a CS student and I am having trouble getting Dev C++ to compile multiple files in a project when working with classes. The problem is that a function prototyped in a class definition won't compile if the function is coded outside of the class. The code attached compiles and runs fine without a project, but does not compile if I try to move it into a project. I get linker errors about multiple definitions. I don't understand why the OOP version is different than a prototype and later function code in a structured program.

Also, I had the same exact problem with code from the Malik textbook (C++ Programming). It also compiled and ran without a project, but failed within a project. I think that the problem is the "project" in some way, not the code, but I am not sure.

I created the project using "File-New-Project-Console Application".

I seem to have two choices: don't use projects, or keep all functions fully inside of the class definitions. Or a third - learn something new?

Here is the code (3 files):

//*******
// FILE NAME: main.cpp
// simple beginnings of a binary tree program
// doesn't do anything yet, but should compile?
//*******

include <iostream>

include <iomanip>

include <cstddef>

include "Tree.cpp"

using namespace std;

int main(int argc, char *argv[])
{

Tree tree;

cout << "***   Binary Trees   ***\n";

system("PAUSE");
return 0;

} // end main()

//*****
// FILE NAME: Tree.cpp
// DESCRIPTION: class
//*****

ifndef TREE

define TREE

include <cstddef>

include "Node.cpp"

using namespace std;

class Tree {

protected:
    Node *root;

public:
    // constructor, creates an empty tree
// Tree() { root = NULL; } // do it this way and it compiles
// if we comment out Tree(); and the function below

Tree(void);  // this version crashes - why?

};

// why doesn't this work in a project?
Tree::Tree(void) {
root = NULL;
}

endif

//******
// FILE NAME: Node.cpp
// DESCRIPTION: class
//******

ifndef NODE

define NODE

include <cstddef>

class Node {

protected:
    Node *left, *right;

public:
    // constructor, creates an empty tree
Node(){ left = right = NULL; }

};

//Node::Node() {
// left = right = NULL;
//}

endif

Thanks.

[vettejeep]

Thanks. It took me a few tries to figure out what you meant, but it worked. I needed to eliminate all #include of cpp files in other cpp files, and keep only the header in both cpp files.

Thanks.

[Anonymous]

Suppose this header:

// header1.h ----------
class myClass {
void method() { /.../} // definition on-line
};
// end header --------

That work fine. Now you declare the method off-line but still in the header:

// header2.h ------------
class myClass {
void method(); // declaration
};
void myClass::method() { /.../} // definition off-line
// end header2 -----------

Here you get an error with "this" compiler (is not enough smart) because each time you include the header there are a new definition of the method. The trickery is to move the definition to a regular .cpp file:

// header3.h -----------
class myClass {
void method(); // declaration
};
// end header3 ----------

// some cpp file --------
void myClass::method() { /.../} // definition off-line
/ some other code here /

// end regular file --------

I'v programmed a lot with BC++, and in such compiler that things does not happen, so your's problem happened to me the first times with this GNU compiler.

HTH

[Anonymous]

Of course, you need include the header3.h in the cpp file.

// some cpp file -------

include header3.h

void myClass::method() { /.../} // definition off-line
/ some other code here /
...

[vettejeep]

Thanks for the replies, but I tried what I think you sugested, and it still does not work for me. The code compiles outside of a formal Dev project, but not inside of a Dev project. Here is new code and the error message:

//*******
// FILE NAME: main.cpp
// simple thing
//*******
// compiles and runs outside of a Dev C++ "project" using Dev C++;
// won't compile inside of a Dev C++ project
// error:
// multile definition of 'Thing::Thing()'
// first defined here
// C:\Dev-Cpp\Examples\Thing\Makefile.win [Build Error] [Thing.exe] Error 1

include <iostream>

include <iomanip>

include "Thing.cpp"

using namespace std;

int main(int argc, char *argv[])
{

Thing thing;

cout << "***   Project Compile Test  ***\n\n";
cout << "Thing is: " << thing.data << endl << endl;

system("PAUSE");
return 0;

} // end main()

//*****
// FILE NAME: Thing.cpp
// DESCRIPTION: class
//*****

ifndef THINGCPP

define THINGCPP

include "Thing.h"

Thing::Thing() {
data = 13;
}

endif

//*****
// FILE NAME: Thing.h
// DESCRIPTION: header
//*****

ifndef THINGH

define THINGH

class Thing {

public:
    int data;  
    Thing();

};

endif

I thought that the whole point of the #ifndef stuff was to prevent multiple inclusions, which don't exist in a program this simple anyway? Sorry, I am still confused.

vettejeep

[Osito]

You need to include Thing.h not Thing.cpp in main. The cpp file will get compiled and linked separately. All you need to include in main is the header file.