Program structure (#include)

Hello.

I was having a problem with a project of mine. I am new to makefiles and I haven't used complicated #include systems, but there appeared a problem with a system of mine:

main.cpp def.h net_funcs.cpp are the files

main.cpp includes def.h
net_funcs.cpp includes def.h

def.h contains some definitions
(main.cpp and net_funcs.cpp both need some of the definitions in the def.h file)

now I have this makefile:

main.exe : main.o net_funcs.o
g++ main.o net_funcs.o -Lc:/cpp/include -lws2_32
main.o : main.cpp
g++ main.cpp -c
net_funcs.o : net_funcs.cpp
g++ net_funcs.cpp -c

when I run make, this will be done:

main.cpp will be compiled (main.o will contain the definitions from def.h)
net_funcs.cpp will be compiled(net_funcs.o will contain the definitions from def.h)
Thus, both files contain the definitions.
when the compiler tries to link them together ( g++ main.o net_funcs.o -Lc:/cpp/include -lws2_32 ) - a clash will occur(double definitions).

So, do you have any ideas of how I should structure my program to make a nice #include system. Is there an universal good style to avoid clashes?

put definitions in the c file
put extern declarations in h-file

(even better - try to avoid global variables)

is there another way? I wouldn't like to use the extern keyword, but if there's not a better way, I'll use it. Thanks anyway.

I need to use global variables like:
const string servername = "www.google.com";

defining them separately in every function that uses the servername, is bothersome

no there is not (except as I said - not using globals)
if you still want global variable
you put
int i = 0; in c-file (there will be 1 instance of this variable)

you put
extern int i;
in h-hile
so every c-file including this h-file knows that somewhere else a global int i variable is defined

what about function declarations?

the extern thingy seemed to work for variables.

in h- file goes

int Myfunc(int,char*,double);

in c-file goes

Code:

---

int Myfunc(int len,char* buffer,double val)
{
  return _snprintf(buffer,len,"%f",val);
}

---