什么时候在全局变量之前使用static关键字？

如果全局变量仅在一个.c文件中可见，则应声明它是静态的。

如果要在多个.c文件中使用全局变量，则不应将其声明为静态。 相反，您应该在需要它的所有.c文件包含的头文件中声明它为extern。

example.h文件

extern int global_foo;

foo.c的

#include "example.h"

int global_foo = 0;
static int local_foo = 0;

int foo_function()
{
   /* sees: global_foo and local_foo
      cannot see: local_bar  */
   return 0;
}

bar.c

#include "example.h"

static int local_bar = 0;
static int local_foo = 0;

int bar_function()
{
    /* sees: global_foo, local_bar */
    /* sees also local_foo, but it's not the same local_foo as in foo.c
       it's another variable which happen to have the same name.
       this function cannot access local_foo defined in foo.c
    */
    return 0;
}