通过多线程或多进程可以减弱阻塞IO的负面作用。

/* For sockaddr_in */#include 
     
      /* For socket functions */#include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
           #define MAX_LINE 16384charrot13_char(char c){ /* We don't want to use isalpha here; setting the locale would change * which characters are considered alphabetical. */ if ((c >= 'a' && c <= 'm') || (c >= 'A' && c <= 'M')) return c + 13; else if ((c >= 'n' && c <= 'z') || (c >= 'N' && c <= 'Z')) return c - 13; else return c;}voidchild(int fd){ char outbuf[MAX_LINE+1]; size_t outbuf_used = 0; ssize_t result; while (1) { char ch; result = recv(fd, &ch, 1, 0); if (result == 0) { break; } else if (result == -1) { perror("read"); break; } /* We do this test to keep the user from overflowing the buffer. */ if (outbuf_used < sizeof(outbuf)) { outbuf[outbuf_used++] = rot13_char(ch); } if (ch == '\n') { send(fd, outbuf, outbuf_used, 0); outbuf_used = 0; continue; } }}voidrun(void){ int listener; struct sockaddr_in sin; sin.sin_family = AF_INET; sin.sin_addr.s_addr = 0; sin.sin_port = htons(40713); listener = socket(AF_INET, SOCK_STREAM, 0);#ifndef WIN32 { int one = 1; setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)); }#endif if (bind(listener, (struct sockaddr*)&sin, sizeof(sin)) < 0) { perror("bind"); return; } if (listen(listener, 16)<0) { perror("listen"); return; } while (1) { struct sockaddr_storage ss; socklen_t slen = sizeof(ss); int fd = accept(listener, (struct sockaddr*)&ss, &slen); if (fd < 0) { perror("accept"); } else { if (fork() == 0) { child(fd); exit(0); } } }}intmain(int c, char **v){ run(); return 0;}
          
         
        
       
      
     

1. 函数 rot13_char(char) 是用来转换字符的，{A,a}~{M,m} -> {N,n}~{Z,z} 其余符号不变

2. server监听端口并响应连接

　　2.1 listener = socket(AF_INET, SOCKET_STREAM, 0) 创建套接字

　　2.2 bind(listener, (sockaddr*)&sin, size(sin)) 绑定套接字到端口

　　2.3 listen(listener, 16) 开始监听

　　2.4 struct sockaddr_storage ss;

　　　   socklen_t slen = sizeof(ss);

　　　   int fd = accept(listener, (struct sockaddr*)&ss, &slen);

　　　　每个fd标识响应的一个请求

　　2.5 if (fork() == 0) {

child(fd); exit(0);}

　　　　创建一个子进程，响应一个请求     

3. server端子进程的处理函数

　　3.1 void child(int fd) 处理函数接口

　　3.2 result = recv(fd, &ch, 1, 0); 从client端读取一个字符

　　       send(fd, outbuf, outbuf_used, 0); 发送一个字符串到client端

注

1. 创建子进程的过程

pid_t pid;     switch (pid = fork())     {     case -1:         perror("The fork failed!";         break;     case 0:         printf("I'm a child!";         system("touch /home/tom/abc.txt";         _exit(0);     default:         printf("Child's pid is %d\n",pid);     }

程序会输出default的内容，并且创建 abc.txt

原因是：创建子进程时，子进程复制了父进程的内容。子进程和父进程同时进入switch语句，但父子进程的pid并不同，因此进入不同的case。