请老师们教教我，请教一个问题

nervfzb

我刚刚接触linux编程，对于fork系统调用不是很理解fork默认返回两个值，一个子进程一个父进程，我在一个程序里一次创建了3个进程，用switch语句判断调用子进程过程和父进程关系，结果返回了12次的值！不知道原因请解释下：）

MMMIX

把完整的代码贴上来。

ynchnluiti

原帖由 nervfzb 于 2009-2-4 23:00 发表
我刚刚接触linux编程，对于fork系统调用不是很理解fork默认返回两个值，一个子进程一个父进程，我在一个程序里一次创建了3个进程，用switch语句判断调用子进程过程和父进程关系，结果返回了12次的值！不知道原因 ...

子进程里也执行fork了吧

nervfzb

源程序:
int main()
{
  pid_t pid1,pid2,pid3;
  pid1=fork();
  pid2=fork();
  pid3=fork();
  switch(pid1)
{
   case 0:
    printf(".....");
   break;
   case -1:
    perror("......");
    breark;
   default:
    printf("....");
    break;
  }
  switch(pid2)
{
   结构同上面一样
}
  switch(pid3)
  {
    结构同上面一样
  }
  return 0;
}

nervfzb

老师们啊，对不起了没有及时发源程序，顶啊，不能沉啦.....

nervfzb

在顶下：)求解答啊

banggou

按LZ贴出的 格式 是应该没有问题的，不知道具体所说的12个值是什么情形的
一个进程打印出4个值还是怎么

nervfzb

#include "stdio.h"
#include "sys/types.h"
#include "unistd.h"
int main()
{
pid_t pid1,pid2,pid3;
int a=1,b=1,c=1;
pid1=fork();
pid2=fork();
pid3=fork();
switch(pid1)
{
  case 0:
  printf("Child process 1 is running.\n");
  a+=4;
  printf("Value a in Child process 1 is:%d\n",a);
  break;
  case -1:
  perror("Child process 1 is failed.\n");
  exit(1);
  default:
  printf("Value a in Parent process is:%d\n",a);
  break;
}
switch(pid2)
{
  case 0:
  printf("Child process 2 is runing.\n");
  b+=4;
  printf("Value b in Child process 2 is:%d\n",b);
  break;
  case -1:
  perror("Child process 1 is failed.\n");
  exit(1);
  default:
  printf("Value b in Parent process is:%d\n",b);
  break;
}
switch(pid3)
{
  case 0:
  printf("Child process 3 is running.\n");
  c+=4;
  printf("Value c in Child process 3 is:%d\n",c);
  break;
  case -1:
perror("Child process 3 is failed.\n");
  exit(1);
  default:
  printf("Value c in Parent process is:%d\n",c);
  break;
}
return 0;
}
这个是完整的代码

下面是编译过程和结果
[root@LinuxFzb tmp]# vi fork5.c
[root@LinuxFzb tmp]# gcc -o fork5 fork5.c
[root@LinuxFzb tmp]# ./fork5
Child process 1 is running.
Value a in Child process 1 is:5
Child process 2 is runing.
Value b in Child process 2 is:5
Child process 3 is running.
Value c in Child process 3 is:5
Child process 1 is running.
Value a in Child process 1 is:5
Child process 2 is runing.
Value b in Child process 2 is:5
Value c in Parent process is:1
Child process 1 is running.
Value a in Child process 1 is:5
Child process 1 is running.
Value a in Child process 1 is:5
Value b in Parent process is:1
Value c in Parent process is:1
Value a in Parent process is:1
Child process 2 is runing.
Value b in Child process 2 is:5
Child process 3 is running.
Value c in Child process 3 is:5
Value a in Parent process is:1
Child process 2 is runing.
Value b in Child process 2 is:5
Value c in Parent process is:1
Value a in Parent process is:1
Value b in Parent process is:1
Child process 3 is running.
Value c in Child process 3 is:5
Value a in Parent process is:1
Value b in Parent process is:1
Value c in Parent process is:1
[root@LinuxFzb tmp]# Value b in Parent process is:1
Child process 3 is running.
Value c in Child process 3 is:5

nervfzb

还望各位老师赏脸看看啊,小弟在此跪谢

ynchnluiti

原帖由 nervfzb 于 2009-2-5 18:04 发表
源程序:
int main()
{
  pid_t pid1,pid2,pid3;
  pid1=fork();
  pid2=fork();
  pid3=fork();
  switch(pid1)
{
   case 0:
    printf(".....");
   break;
   case -1:
    perror("......") ...

pid2=fork();
pid3=fork();
不止执行一次