atexit函数 exit 和＿exit 的区别

进程退出方式：

１．正常结束：

１）main  函数结束；

２）exit（３） 结束：调用atexit (3) ,  on_exit  (3) 函数．    

  All open stdio(3) streams are flushed and closed.  Files created by tmpfile(3) are removed.

３）_exit(2) 结束：不会调用atexit  on_exit函数

 The function _exit() terminates the calling process "immediately".  Any open file descriptors belong‐
       ing to the process are closed; any children of the process are inherited by process 1, init, and  the
       process's parent is sent a SIGCHLD signal.

２．非正常结束：

１）信号结束：

２）abort函数：实际上也是给发送一个SIGABRT信号．

atexit函数的测试代码：

#include <iostream>#include <stdlib.h>using namespace std;void atexit1(){    cout <<  "in 1" << endl;}void atexit2(){    cout <<  "in 2" << endl;}int main(){    atexit(atexit1);    atexit(atexit2);    cout << "before end" << endl;    return -1;}

 ./testretval
before end
in 2
in 1