I have a question on external variables in a multifile program.
Quoting from K&R (first addition, page 72)
"By default, external variables are also "global", so that all references to such a variable by the same name (even from functions compiled separately) are references to the same thing."
Here's an example that doesn't work. The variable 'a' in file 1 is external (since it's defined outside of any function) so, according to the above paragraph, it should have the same value in file 2. The
program, however, doesn't compile. If the line "int a" is added to
file 2 it compiles and runs, giving the wrong answer 0. If instead the
line "extern int a" is added then it runs and gives the correct
answer 12. I understand why the last version works, but shouldn't
the first one also (according to K&R)?
Does anyone have any insights to offer?
_____________________file 1____________________________
#include <iostream>
using namespace std;
int a=6;
int f(int);
main()
{ cout << f(2) << endl;
}
________________file 2____________________________
int f(int x)
{ return (a*x);
} 
