c - 全局值无法在另一个文件中访问？

Question

这个问题已经有答案了:

How do I use extern to share variables between source files? (19 个回答)

已关闭 8 年前。

全局值无法在另一个文件中访问？我的代码如下，请帮我修复

flie1.c

 #include<stdio.h>
 extern int i=9;  
  int main()
 {
   printf("i m in main\n");
 }

文件2.c

  printf("%d\n",i);

我正在将两个文件同时编译为 cc file1.c file2.c

Answer 1

像这样改变它，它就会起作用:

文件1.c

#include <stdio.h>
int i = 9; // define the variable
void print(); // declare print: say there is a function called `print` with no arguments and no return type (because the function is DEFINED in file2.c)

int main() {
     printf("im in main");
     print();
     return 0;
}

文件2.c

extern int i; // declare "i": say there is a variable called `i` with type of `int` (because the variable is DEFINED in file1.c)

void print() { 
     printf("%d\n", i);
}