Multiple Source Files, make files, scope, include

I'm working on a little program and I want to break it up into multiple source files and also use a make file. I can't seem to get my program to compile though and I don't know why. I type

Code:

mingw32-make -f makefile.mak

and it doesn't compile. Here are some source files that illustrate my problem.

Code:

// main.cpp
#include <iostream>
using namespace std;

int main () {
  CPoint A, B;
  A.set_point (3,4);
  B.set_point (5,-2);
  cout << "distance between points: " << distance(A, B) << endl;
  return 0;
}

Code:

// CPoint.cpp
#include <cmath>

class CPoint {
    double x, y;
  public:
    void set_point (double,double);
    double distance(CPoint,CPoint);
};


void CPoint::set_point (double a, double b) {
  x = a;
  y = b;
}

double CPoint::distance (CPoint A, CPoint B){
	double dist;
	
	dist = sqrt((A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y));
	
	return dist;	
}

Code:

#makefile.mak
all: Mult

Mult: main.o CPoint.o
	g++ main.o CPoint.o -o Mult

main.o: main.cpp
	g++ -c main.cpp
	
CPoint.o: CPoint.cpp
	g++ -c CPoint.cpp	
			
clean:
	rm -rf *o Mult

Well, distance is a member function of CPoint. So you have to call it via A.distance(...), or B.distance(...). Might be better to change the function name to distance_to( CPoint ) so you would call it like A.distance_to( B ); then get rid of all the A.'s in the implementation of the distance function.

main() doesn't know about CPoint. The declarations and type definitions must be available. Put the definition of CPoint into a new header file CPoint.hpp and include it from all .cpp files that need it.

Also, there's no need to be so explicit in makefiles. Given built-in pattern rules and all that, your current makefile could be written as:

Code:

#makefile.mak
all: Mult

Mult: main.o CPoint.o
			
clean:
	rm -rf *.o Mult

.PHONY: all clean

Note also the lack of a dot in your clean rule.

Originally Posted by twomers

Well, distance is a member function of CPoint. So you have to call it via A.distance(...), or B.distance(...). Might be better to change the function name to distance_to( CPoint ) so you would call it like A.distance_to( B ); then get rid of all the A.'s in the implementation of the distance function.

You also probably should remove one of the arguments of distance, so that it uses the object used to call distance, e.g.

Code:

a.Distance(b);

As an alternative, you could make a distance function that takes two CPoint arguments, that is a friend function of CPoint (it needs to be a friend so that it can get to the CPoint private data).

--
Mats

Originally Posted by CornedBee

main() doesn't know about CPoint. The declarations and type definitions must be available. Put the definition of CPoint into a new header file CPoint.hpp and include it from all .cpp files that need it.

I presume that member functions would be placed in a third .cpp file that must be included somewhere, no?

Code:

#makefile.mak
all: Mult

Mult: main.o CPoint.o
			
clean:
	rm -rf *.o Mult

.PHONY: all clean

Note also the lack of a dot in your clean rule.

Is this true on *nix systems as well?

Originally Posted by thetinman

I presume that member functions would be placed in a third .cpp file that must be included somewhere, no?

No, the member functions stay in the second source file. And you never include source files.

Is this true on *nix systems as well?

It's a feature of GNU make and some other makes.

I'm made some changes, but am still having problems. My files are now

Code:

# makefile.mak
all: Mult

Mult: main.o CPoint.o
            g++ main.o CPoint.o -o Mult

main.o: main.cpp
            g++ -c main.cpp
          
CPoint.o: CPoint.hpp
            g++ -c CPoint.hpp         
                                   
clean:
            rm -rf *.o Mult
          
.PHONY: all clean

Code:

// main.cpp
#include <iostream>
#include "CPoint.hpp"

using namespace std;

int main () {
  CPoint A, B;
  A.set_point (3,4);
  B.set_point (5,-2);
  return 0;
}

Code:

// CPoint.hpp
#include <cmath>

class CPoint {
    double x, y;
  public:
    void set_point (double,double);
};


void CPoint::set_point (double a, double b) {
  x = a;
  y = b;
}

set_point looks very much like it should be the constructor to me.

--
Mats

You've abandoned CPoint.cpp, which is where set_point and all other out-of-line implementations belong.

You cannot compile a header file. You can only compile source files. Header files are included.

In addition, header files should be listed in the dependencies. Your makefile then becomes:

Code:

# makefile.mak
all: Mult

Mult: main.o CPoint.o

main.o: main.cpp CPoint.hpp
          
CPoint.o: CPoint.cpp CPoint.hpp
                                   
clean:
            rm -rf *.o Mult
          
.PHONY: all clean

It's possible to auto-generate the dependency information, but that's rather complicated and not worth it for a small project.

Why is a header file included if it is not getting compiled?

Why is a header file included if it is not getting compiled?

Because it becomes part of a translation unit (source file + headers and source files that it includes) that is compiled.

The contents of header files are just pasted into where '#include "x.h"' is located.
Thus they actually end up in the actual .cpp files.
Header files should contain declarations and class definitions and things like that.
Like to make the compiler understand there's a CPoint class, you must give it the CPoint class definition before its usage. To avoid code duplication, you put it inside a header file and include it via #include in all source files that use the class.

I'm just trying to compile without the makefile. My files look like this:

Code:

// main.cpp
#include <iostream>
#include "CPoint.hpp"

using namespace std;

int main () {
  CPoint A, B;
  A.set_point (3,4);
  B.set_point (5,-2);
  return 0;
}

This is the strange looking one:

Code:

// CPoint.hpp

class CPoint {
    double x, y;
  public:
    void set_point (double,double);
};

#include "CPoint.cpp"

Code:

// CPoint.cpp

void CPoint::set_point (double a, double b) {
  x = a;
  y = b;
}

In the strange one, I have to put the statement

Code:

#include "CPoint.cpp"

after the primary section of code to prevent compilation errors. This placement looks strange to me, and I suspect that it is bad form - Is it bad form?

Don't include source code.

But then again, you've never actually posted any error messages either. Only the useless refrain "it doesn't work".

CPoint.cpp includes CPoint.hpp (not as you have it).

Then from the command line, it's
g++ CPoint.cpp main.cpp

Or the makefile in your original post.