如何创建一个后台进程

 1 #include <iostream>
 2 #include <unistd.h>
 3 using namespace std;
 4 
 5 void print() 
 6 {
 7     int pid = getpid();
 8     int gid = getpgid(0);
 9     cout << "process group id = " << gid << endl;
10     cout << "process id = " << pid << endl;
11 }
12 
13 int main() 
14 {
15     //create a child process.
16     int pid = fork();
17     if (-1 == pid) 
18     {
19         cout << "call function fork() error!" << endl;
20     }
21     else if (0 == pid)     //return from child process.
22     {
23         cout << "----------in child process.----------" << endl;
24         print();
25         cout << "--------------------------------------" << endl;
26         //将该进程的进程组ID设置为该进程的进程ID。
27         setpgrp();
28         cout << "----------in child process. setpgrp()----------" << endl;
29         print();
30         cout << "--------------------------------------" << endl;
31         //创建一个新的Session，断开与控制终端的关联。也就是说Ctrl+c的触发的SIGINT信号，该进程接收不到。
32         setsid();
33 
34     
35         for (int i = 0; i < 5; ++i) 
36         {
37             sleep(20);
38             cout << "----------in child process.----------" << endl;
39             print();
40             cout << "--------------------------------------" << endl;
41         }
42     }
43     else             //return from parent process.
44     {
45         cout << "----------in parent process.----------" << endl;
46         print();
47         cout << "--------------------------------------" << endl;
48     }
49     return 0;
50 }