atexit函数

NAME
atexit - register a function to be called at normal process termination

　　 函数的正常结束时候调用。当一个函数被kill命令杀死，或是使用其他方式总结如ctrl+C方式终结时，这个是不被调用的。

SYNOPSIS
#include <stdlib.h>

int atexit(void (*function)(void));

DESCRIPTION
The atexit() function registers the given function to be called at nor‐
mal process termination, either via exit(3) or via return from the pro‐
gram's main(). Functions so registered are called in the reverse order
of their registration; no arguments are passed.
调用时注册的反向调用。C++的析构函数和构造函数就是与这个类似，估计C++多少受到这个影响。
The same function may be registered multiple times: it is called once
for each registration.

POSIX.1-2001 requires that an implementation allow at least ATEXIT_MAX
(32) such functions to be registered. The actual limit supported by an
implementation can be obtained using sysconf(3).

When a child process is created via fork(2), it inherits copies of its
parent's registrations. Upon a successful call to one of the exec(3)
functions, all registrations are removed.

RETURN VALUE
The atexit() function returns the value 0 if successful; otherwise it
returns a nonzero value.

#include"apue.h"
static void my_exit1(void);
static void my_exit2(void);

int main()
{
if(atexit(my_exit2) != 0)
err_sys("can not register my_exit2\n");
if(atexit(my_exit1) != 0)
err_sys("can not register my_exit1\n");
if(atexit(my_exit1) != 0)
err_sys("can not register my_exit1\n");
printf("main is done\n");
while(1);
return 0;

printf("main has exited!\n");

}
static void my_exit1(void){
printf("first exit handler\n");
}
static void my_exit2(void){
printf("second exit handler\n");
}

该程序使用Ctrl+C或是kill命令杀死上述程序的时候，没有任何注册函数的打印信息。

该函数作为很好的一个调试接口或是很好定位手段。