Internal static variables in C, would you use them

Question

In C you can have external static variables that are viewable every where in the file, while internal static variables are only visible in the function but is persistent

For example:

#include <stdio.h>

void foo_bar( void )
{
        static counter = 0;
        printf("counter is %d\n", counter);
        counter++;
}
int main( void )
{
        foo_bar();
        foo_bar();
        foo_bar();
 return 0;
}

the output will be

counter is 0
counter is 1
counter is 2

My question is why would you use an internal static variable? If you don't want your static variable visible in the rest of the file shouldn't the function really be in its own file then?

Answer 1

I wouldn't want the existence of a static variable to force me to put the function into its own file. What if I have a number of similar functions, each with their own static counter, that I wanted to put into one file? There are enough decisions we have to make about where to put things, without needing one more constraint.