iOS Socket编程-C语言版（UDP）

本篇文章为总结使用C语言的api来完成UDP通信的基本功能，如果您对Socket不了解，请先阅读上一篇理论知识：

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1. UDP Socket编程

先讲一讲UDP编程，因为比TCP要简单多了。首先，我们需要明白UDP是用户数据报协议，英文名为User Datagram Protocol，它是面向无连接的。

注意：Socket通信一定有要服务端和客户端。

1.1 UDP Socket客户端

客户端的工作流程：首先调用socket函数创建一个Socket，然后指定服务端的IP地址和端口号，就可以调用sendto将字符串传送给服务器端，并可以调用recvfrom接收服务器端返回的字符串，最后关闭该socket。

笔者这里分成了四步：

1. 第一步：创建socket并配置socket，如服务端ip地址和端口号
2. 第二步：调用sendto发送消息到服务器端
3. 第三步：调用recvfrom接收来自服务器端的消息
4. 第四步：调用close关闭socket

1.1.1 客户端的代码实现：

- (void)udpClient {  int clientSocketId;  ssize_t len;  socklen_t addrlen;  struct sockaddr_in client_sockaddr;  char buffer[256] = "Hello, server, how are you?";  // 第一步：创建Socket  clientSocketId = socket(AF_INET, SOCK_DGRAM, 0);  if(clientSocketId < 0) {    NSLog(@"creat client socket fail\n");    return;  }  addrlen = sizeof(struct sockaddr_in);  bzero(&client_sockaddr, addrlen);  client_sockaddr.sin_family = AF_INET;  client_sockaddr.sin_addr.s_addr = inet_addr("192.168.1.107");  client_sockaddr.sin_port = htons(1024);  int count = 10;  do {    bzero(buffer, sizeof(buffer));    sprintf(buffer, "%s", "Hello, server, how are you?");    // 第二步：发送消息到服务端    // 注意:UDP是面向无连接的，因此不用调用connect()    // 将字符串传送给server端   len = sendto(clientSocketId, buffer, sizeof(buffer), 0, (struct sockaddr *)&client_sockaddr, addrlen);    if (len > 0) {      NSLog(@"发送成功");    } else {      NSLog(@"发送失败");    }    // 第三步：接收来自服务端返回的消息    // 接收server端返回的字符串    bzero(buffer, sizeof(buffer));    len = recvfrom(clientSocketId, buffer, sizeof(buffer), 0, (struct sockaddr *)&client_sockaddr, &addrlen);    NSLog(@"receive message from server: %s", buffer);    count--;  } while (count >= 0);  // 第四步：关闭socket  // 由于是面向无连接的，消息发出处就可以了，不用管它收不收得到，发完就可以关闭了  close(clientSocketId);}

1.1.2 客户端的打印日志

2015-12-06 15:38:36.095 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.286 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.286 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.291 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.291 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.296 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.296 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.316 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.317 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.324 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.324 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.328 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.329 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.339 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.339 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.355 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.356 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.366 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.366 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.372 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?2015-12-06 15:38:36.373 iOS-Socket-C-Version-Client[9709:4234848] 发送成功2015-12-06 15:38:36.392 iOS-Socket-C-Version-Client[9709:4234848] receive message from server: Hello, server, how are you?

1.2 UDP Socket服务器端

服务器端的工作流程：首先调用socket函数创建一个套接字，然后调用bind函数将其与本机地址以及一个本地端口号绑定，接收到一个客户端时，服务器显示该客户端的IP地址，并将字串返回给客户端。

笔者这里分成了五步：

1. 第一步：创建socket并配置socket
2. 第二步：调用bind绑定服务器本机ip及端口号
3. 第三步：调用recvfrom接收来自客户端的消息
4. 第四步：调用sendto将接收到服务器端的信息返回给客户端
5. 第四步：调用close关闭socket

1.2.1 服务器端代码实现

- (void)udpServer {  int serverSockerId = -1;  ssize_t len = -1;  socklen_t addrlen;  char buff[1024];  struct sockaddr_in ser_addr;  // 第一步：创建socket  // 注意，第二个参数是SOCK_DGRAM，因为udp是数据报格式的  serverSockerId = socket(AF_INET, SOCK_DGRAM, 0);  if(serverSockerId < 0) {    NSLog(@"Create server socket fail");    return;  }  addrlen = sizeof(struct sockaddr_in);  bzero(&ser_addr, addrlen);  ser_addr.sin_family = AF_INET;  ser_addr.sin_addr.s_addr = htonl(INADDR_ANY);  ser_addr.sin_port = htons(1024);  // 第二步：绑定端口号  if(bind(serverSockerId, (struct sockaddr *)&ser_addr, addrlen) < 0) {    NSLog(@"server connect socket fail");    return;  }  do {    bzero(buff, sizeof(buff));    // 第三步：接收客户端的消息    len = recvfrom(serverSockerId, buff, sizeof(buff), 0, (struct sockaddr *)&ser_addr, &addrlen);    // 显示client端的网络地址    NSLog(@"receive from %s\n", inet_ntoa(ser_addr.sin_addr));    // 显示客户端发来的字符串    NSLog(@"recevce:%s", buff);    // 第四步：将接收到的客户端发来的消息，发回客户端    // 将字串返回给client端    sendto(serverSockerId, buff, len, 0, (struct sockaddr *)&ser_addr, addrlen);  } while (strcmp(buff, "exit") != 0);  // 第五步：关闭socket  close(serverSockerId);}

1.2.2 服务器端的打印日志

2015-12-06 15:38:36.268 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.269 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.372 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.372 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.377 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.377 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.382 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.382 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.405 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.405 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.409 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.410 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.414 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.415 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.425 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.426 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.441 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.441 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.452 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.452 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?2015-12-06 15:38:36.472 iOS-Socket-C-Version-Server[39130:2473780] receive from 192.168.1.1002015-12-06 15:38:36.473 iOS-Socket-C-Version-Server[39130:2473780] recevce:Hello, server, how are you?

我们这里打印出了客户端发来的消息，由于上面实现的代码中，只发10次，所以这里只有10条。

源代码

小伙伴们，可以到github下载了：

注意：这里面有两个工程，一个是客户端，一个是服务器端。运行时，先运行服务器端，然后再选择客户端。另外，客户端所指定的服务器端的ip地址一定要修改成您本机对应的ip，不然使用笔者这里的ip就会失败。

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