无连接通信

 

无连接通信是通过UDP/IP协议完成的。数据的传输利用数据包，即离散信息包。

int recvfrom(
  SOCKET s,
  char FAR* buf,
  int len,
  int flags,
  struct sockaddr FAR* from,
  int FAR* fromlen
);

int WSARecvfrom(
  SOCKET s,
  LPWSABUF lpBuffers,
  DWORD dwBufferCount,
  LPDWORD lpNumberOfBytesRecvd,
  LPDWORD lpFlags,
  struct sockaddr FAR* lpfrom,
  LPINT  fromlen,
  LPWSAOVERLAPPED lpOverlapped,
  LPWSAOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine
);

创建一个简单的接收端应用程序

#include<winsock2.h>

void main(void)
{
  WSADATA wsaData;
  SOCKET s;
  SOCKADDR_IN Recvaddr;
  SOCKADDR_IN Sendaddr;
  int port = 5050;
  char buffer[1024];
  int buflen = 1024;
  int sendaddrsize = sizeof(Sendaddr);

  WSAStartup(MAKEWORD(2,2), &wsaData);
  s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
  Recvaddr.sin_family = AF_INET;
  Recvaddr.sin_port = htons(port);
  Recvaddr.sin_addr.s_addr = htonl(INADDR_ANY);
  bind(s, (SOCKADDR *)&Recvaddr, sizeof(Recvaddr));

  recvfrom(s, buffer, buflen, 0, (SOCKADDR*)&Sendaddr, &sendaddrsize);
  closesocket(s);
  WSACleanup();
}

发送端

int sendto(
  SOCKET s,
  const char FAR* buf, //发送数据的缓冲区
  int len, //指明发送多少字节
  int flag,
  const sockaddr FAR* to,
  int tolen
);

int WSASendto(
  SOCKET s,
  LPWSABUF lpBuffers,
  DWORD dwBufferCount,
  LPDWORD lpNumberOfBytesSend,
  LPDWORD lpFlags,
  struct sockaddr FAR* lpto,
  LPINT  tolen,
  LPWSAOVERLAPPED lpOverlapped,
  LPWSAOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine
);

 

简单的发送端程序

#include <winsock2.h>

void main(void)
{
  WSADATA wsaData;
  SOCKET s;
  SOCKADDR_IN addr;
  int port = 5050;
  char buffer[1024];
  int len = 1024;

  WSAStartup(MAKEWORD(2,2), &wsaData);
  s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
  addr.sin_family = AF_INET;
  addr.sin_port = htons(port);
  addr.sin_addr.s_addr = inet_addr("123.123.123.123");

  sendto(s, buffer, len, 0, (SOCKADDR*)&addr, sizeof(addr));
  closesocket(s);
  WSACleanup();
}

 

因为无连接协议没有连接，所有也不会有对连接的正式关闭和从容关闭。只需要调用closesocket即可释放资源。