Test case: Code for c1.c:

#include <stdio.h>
 
static int stat;
 
int getSetStat1(int n) {
    int v = stat;
    stat = n;
    return v;
}
 
int main(void) {
    getSetStat2(4);
    getSetStat1(3);
    printf("stat.1=%i, stat.2=%i\n",stat, getSetStat2(5));
    return 0;
}

Code for c2.c:

static int stat;
 
int getSetStat2(int n) {
    int v = stat;
    stat = n;
    return v;
}

Compile with gcc c2.c c1.c. Output: stat.1=3, stat.2=4.