<二>、进程-(eixt)(_exit)(atexit)(exec)

《exit函数实现》

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

int main (void )
{
 pid_t ret;

 printf("hello!\n");
 
   printf("In parent process, pid =%d", getpid());
 exit(0); 
 return 0;
}

结果：

hello!
In parent process, pid =3342
********************************************************

《_exit函数实现》

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

int main (void )
{
 pid_t ret;

 printf("hello!\n");
 printf("22hello!\n");
 printf("two hello!");
   printf("In parent process, pid =%d", getpid());
 _exit(0); 
 printf(" e next hello!\n");
 printf(" e frok hello!");
 return 0;
}

结果：
hello!
22hello!

********************************************************

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
void exit_func1(void)
{
 printf("exit_func1\n");
}

void exit_func2(void)
{
        printf("exit_func2\n");
}

int main (void )
{
// pid_t ret;

 printf("hello!\n");

 atexit(exit_func1);
 atexit(exit_func2);

   printf("In parent process, pid =%d", getpid());
 exit(0); 
 printf("newver be dispalyed\n");
 return 0;
}

结果：

hello!
In parent process, pid =3554exit_func2
exit_func1

-----------

main主函数执行完毕后，是否可能会再执行一段代码？
如果需的话，可以用ateixt()函数注册一个函数：
 1 #include<stdio.h>
  2 #include<stdlib.h>
  3
  4 void fumc1()
  5 {printf("next\n");}
  6
  7 void fumc2()
  8 {printf("executed");}
  9 void fumc3()
 10 {printf("is");}
 11 void fumc4()
 12 {printf("this");}
 13
 14 void main()
 15 {
 16     char str[]="0123456789";
 17 atexit(fumc1);
 18 atexit(fumc2);
 19 atexit(fumc3);
 20 atexit(fumc4);
 21 printf("This is execued frist. \n");
 22 printf("%d\n",sizeof(str));
 23}
结果：
This is execued frist.
11
thisisexecutednext
本来到该结束程序printf("%d\n",sizeof(str));，
但是还打印thisisexecutednext
说明：该程序结束后，还运行atexit函数
而且到过来运行
****************************************************

《exec函数实现》

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
int main (void )
{ pid_t ret;
 printf("hello!\n");
 ret = fork();
 printf("Have forked!\n");
 if (ret < 0 ) {
  perror("fork");
  exit(1); }
 if (ret == 0 ) {  //子进程  
//printf("In child process, pid=%d, ppid=%d\n", getpid(), getppid());
  if (execl("/bin/ls", "ls", "-al", NULL) <0 ) {
   perror("execl error!");
   exit(1); 
  }
  printf("Can't run to here in normal!\n");
//     execlp("ls", "ls", "-al", NULL);
   exit(0); }
 sleep(5);
   printf("In parent process, pid =%d, child pid=%d\n", getpid(), ret);
 return 0;
}

结果：

hello!
Have forked!
Have forked!
total 108
drwxrwxrwx 2 nobody nogroup  4096 2011-12-07 18:06 .
drwxrwxrwx 9 lsb    lsb      4096 2011-12-07 18:00 ..
-rwxr--r-- 1 nobody nogroup   380 2011-07-20 23:58 atexit.c
-rwxr-xr-x 1 lsb    lsb      7861 2011-12-07 02:33 c
-rwxr--r-- 1 nobody nogroup  3527 2011-12-07 02:33 c.c
-rwxr-xr-x 1 lsb    lsb      7350 2011-12-07 18:06 exec
-rwxr--r-- 1 nobody nogroup   601 2011-07-20 23:47 exec.c
-rwxr-xr-x 1 lsb    lsb      7202 2011-12-07 18:04 exit
-rwxr--r-- 1 nobody nogroup   193 2011-07-20 23:51 _exit.c
-rwxr--r-- 1 lsb    lsb       194 2011-12-07 18:04 exit.c
-rwxrwxrwx 1 root   root     7350 2011-12-07 02:20 fork
-rwxrwxrwx 1 nobody nogroup   502 2011-07-20 23:40 fork.c
prw-r--r-- 1 lsb    lsb         0 2011-12-07 02:30 in1
prw-r--r-- 1 lsb    lsb         0 2011-12-07 02:30 in2
-rwxr-xr-x 1 lsb    lsb      7508 2011-12-07 02:26 pipe
-rwxrwxrwx 1 nobody nogroup  1378 2008-12-19 03:17 pipe.c
-rwxr-xr-x 1 lsb    lsb      7528 2011-12-07 02:30 pipe_select
-rwxr--r-- 1 nobody nogroup  3029 2008-12-19 03:17 pipe_select.c
-rwxr-xr-x 1 lsb    lsb     12180 2011-12-07 02:35 s
-rwxr--r-- 1 nobody nogroup  4865 2011-12-07 02:32 s.c
In parent process, pid =3157, child pid=3158
************************************************************************