无连接通信

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
);

#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();
}

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
);

#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();
}