管道通信pipe()实验

父进程创建两个子进程，子进程通过管道向父进程传递消息。父进程先读子进程1的，再读子进程2的。

 1 #include <sys/wait.h>
 2 #include <sys/types.h>
 3 #include <unistd.h>
 4 #include <iostream>
 5 #include <cstdlib>
 6 #include <signal.h>
 7 #include <string>
 8 using namespace std;
 9 int flag;
10 void foo (int signo) {
11     flag = 0;
12 }
13 int main() {
14     int fp[2];
15     pid_t pid1, pid2;
16     string InPipe;
17     string OutPipe;
18     while ( pipe(fp) < 0 );
19     if ( (pid1 = fork()) < 0 ) {
20         cout << "pid1 error" << endl;
21         return -1;
22     }
23     if (pid1 == 0) {
24         flag = 1;
25         signal(16, foo);
26         while(flag);
27         close(fp[0]);
28         InPipe = "C1";
29         write(fp[1], InPipe.c_str(), InPipe.length()+1);
30         sleep(1);
31         exit(0);
32     }
33     else {
34         if ( (pid2 = fork()) < 0 ) {
35             cout << "pid2 error" << endl;
36             return -1;
37         }
38         if (pid2 == 0) {
39             flag = 1;
40             signal(17, foo);
41             while(flag);
42             close(fp[0]);
43             InPipe = "C2";
44             write(fp[1], InPipe.c_str(), InPipe.length()+1);
45             sleep(1);
46             exit(0);
47         }
48         else {
49             sleep(5);
50             char c = '0';
51             close(fp[1]);
52             kill(pid1, 16);
53             waitpid(pid1, 0, 0);
54             OutPipe.clear();
55             while (read(fp[0], &c, 1) && c != '\0')
56                 OutPipe += c;
57             cout << OutPipe << endl;
58             kill(pid2, 17);
59             waitpid(pid2, 0, 0);
60             OutPipe.clear();
61             c = '0';
62             while (read(fp[0], &c, 1) > 0 && c != '\0')
63                 OutPipe += c;
64             cout << OutPipe << endl;
65             exit(0);
66         }
67     }
68     return 0;
69 }

发送信号告诉两个子进程向管道写数据，等到子进程结束，再从管道读取。

把L52,L53分别和L58,L59互换，就实现了先读进程1，再读进程2。