将extern用于全局变量的正确方法是什么？

#include<stdio.h>

int global_var = 10;

int main() {
   printf("Global variable: %d\n", global_var);
   return 0;
}

#include<stdio.h>

extern int global_var;

void print_global_var() {
   printf("Global variable in other.c: %d\n", global_var);
}

#include "other.c"

int main() {
   printf("Global variable: %d\n", global_var);
   print_global_var();
   return 0;
}