test_static.c

#include <assert.h>
#include <stdio.h>

enum { N = 10 };

static void inc(int* static_out, int* out){
  static int static_var = 0;
  int var = 0;
  ++static_var;
  ++var;
  printf("static_var=%d, var=%d\n", static_var, var);
  *static_out = static_var;
  *out = var;
}

int main(void) {
  int i = 0;
  int ret = -1;
  int static_ret = -1;
  for ( ; i < N; ++i)
    inc(&static_ret, &ret);
  assert(ret == 1);
  assert(static_ret == N);
}