Chapter 8 Drill 1 : undefined reference to foo

[JS]

I've met a problem when trying to compile chapter 8 drill 1. I did everything that the book tells me but I can't figure what's wrong

//my.h
extern int foo;
void print_foo();
void print(int);

//my.cpp
#include "my.h"
#include "../std_lib_facilities.h"


void print_foo(){
    cout << foo;
}
void print(int i){
    cout << i;
}

//use.cpp
#include "my.h"

int main(){
    foo = 7;
    print_foo();
    print(99);
   
}

the error i got
use.cpp:4: undefined reference to `foo'
my.cpp:6: undefined reference to `foo'

All files are in the same directory.

Can anyone help please?

[Christiano]

You should try this:

//my.h
extern int foo;
void print_foo();
void print(int);

//my.cpp
#include "my.h"
#include "../std_lib_facilities.h"



int foo;



void print_foo(){
    cout << foo;
}
void print(int i){
    cout << i;
}

//use.cpp
#include "my.h"

int main(){
    foo = 7;
    print_foo();
    print(99);
   
}


Because "extern int foo" works as a declaration, and "int foo" works as a definition.

Does it solve the problem?

[JS]

That worked, thanks.