UDP组播是基于IP多播技术实现的。IP多播是一种将数据包从一个源地址同时传输到多个目的地址的技术。在IP多播中，源地址标识了数据包发送方的IP地址，目的地址标识了多播组的IP地址。多播组的IP地址通常是一个特殊的地址，即D类IP地址（224.0.0.0～239.255.255.255）。多播组的地址由网络管理员分配，用于标识一个多播组。

UDP多播的原理是，将数据包从一个源地址同时传输到多个目的地址。数据包在传输过程中不需要建立连接，因此发送速度快，但可靠性低。UDP多播可以通过指定多播地址来进行多播，多播地址是D类IP地址。

讯享网

以下是VC多线程实现UDP组播的发送和接收程序代码：

发送端代码：

#include <stdio.h> #include <winsock2.h> #pragma comment(lib, "ws2_32.lib") int main() { WSADATA wsaData; int retVal; // Initialize Winsock retVal = WSAStartup(MAKEWORD(2, 2), &wsaData); if (retVal != 0) { printf("WSAStartup failed: %d ", retVal); return 1; } // Create a [socket](https://wenku.csdn.net/doc/6412b76abe7fbd1778d4a37f?spm=1055.2569.3001.10083) for sending data SOCKET SendSocket; SendSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); if (SendSocket == INVALID_SOCKET) { printf("socket failed: %ld ", WSAGetLast[error](https://wenku.csdn.net/doc/6401acf5cce7214c316edc34?spm=1055.2569.3001.10083)()); WSACleanup(); return 1; } // Set the TTL value for the outgoing packets int TTL = 2; retVal = setsockopt(SendSocket, IPPROTO_IP, IP_[multi](https://wenku.csdn.net/doc/42gucd32s6?spm=1055.2569.3001.10083)CAST_TTL, (char*)&TTL, sizeof(TTL)); if (retVal == SOCKET_ERROR) { printf("setsockopt failed: %d ", WSAGetLastError()); closesocket(SendSocket); WSACleanup(); return 1; } // Set up the destination [address](https://wenku.csdn.net/doc/6412b59abe7fbd1778d43bdb?spm=1055.2569.3001.10083) for sending the multicast message char* MulticastAddr = "239.255.1.1"; struct sockaddr_in DestAddr; DestAddr.sin_family = AF_INET; DestAddr.sin_addr.s_addr = inet_addr(MulticastAddr); DestAddr.sin_port = htons(1234); // Send the multicast message using multiple threads const int NumThreads = 4; HANDLE hThreads[NumThreads]; for (int i = 0; i < NumThreads; i++) { hThreads[i] = CreateThread(NULL, 0, SendThreadFunc, (LPVOID)&SendSocket, 0, NULL); if (hThreads[i] == NULL) { printf("CreateThread failed: %d ", GetLastError()); closesocket(SendSocket); WSACleanup(); return 1; } } // Wait for all threads to terminate WaitForMultipleObjects(NumThreads, hThreads, TRUE, INFINITE); // Close the socket and clean up Winsock closesocket(SendSocket); WSACleanup(); return 0; } DWORD WINAPI SendThreadFunc(LPVOID lpParam) { SOCKET* pSendSocket = (SOCKET*)lpParam; // Send a multicast message char* MulticastMsg = "Hello, world!"; const int MsgLen = strlen(MulticastMsg); int retVal = sendto(*pSendSocket, MulticastMsg, MsgLen, 0, (struct sockaddr*)&DestAddr, sizeof(DestAddr)); if (retVal == SOCKET_ERROR) { printf("sendto failed: %d ", WSAGetLastError()); return 1; } return 0; } 

接收端代码：

讯享网#include <stdio.h> #include <winsock2.h> #pragma comment(lib, "ws2_32.lib") int main() { WSADATA wsaData; int retVal; // Initialize Winsock retVal = WSAStartup(MAKEWORD(2, 2), &wsaData); if (retVal != 0) { printf("WSAStartup failed: %d ", retVal); return 1; } // Create a socket for receiving data SOCKET RecvSocket; RecvSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); if (RecvSocket == INVALID_SOCKET) { printf("socket failed: %ld ", WSAGetLastError()); WSACleanup(); return 1; } // Bind the socket to the local address struct sockaddr_in LocalAddr; LocalAddr.sin_family = AF_INET; LocalAddr.sin_addr.s_addr = htonl(INADDR_ANY); LocalAddr.sin_port = htons(1234); retVal = bind(RecvSocket, (struct sockaddr*)&LocalAddr, sizeof(LocalAddr)); if (retVal == SOCKET_ERROR) { printf("bind failed: %d ", WSAGetLastError()); closesocket(RecvSocket); WSACleanup(); return 1; } // Join the multicast group char* MulticastAddr = "239.255.1.1"; struct ip_mreq Mreq; Mreq.imr_multiaddr.s_addr = inet_addr(MulticastAddr); Mreq.imr_[interface](https://wenku.csdn.net/doc/6412b49ebe7fbd1778d40370?spm=1055.2569.3001.10083).s_addr = htonl(INADDR_ANY); retVal = setsockopt(RecvSocket, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*)&Mreq, sizeof(Mreq)); if (retVal == SOCKET_ERROR) { printf("setsockopt failed: %d ", WSAGetLastError()); closesocket(RecvSocket); WSACleanup(); return 1; } // Receive multicast messages while (true) { char RecvBuf[1024]; struct sockaddr_in SenderAddr; int SenderAddrLen = sizeof(SenderAddr); int NumBytes = recvfrom(RecvSocket, RecvBuf, sizeof(RecvBuf), 0, (struct sockaddr*)&SenderAddr, &SenderAddrLen); if (NumBytes == SOCKET_ERROR) { printf("recvfrom failed: %d ", WSAGetLastError()); break; } else { RecvBuf[NumBytes] = '0'; printf("Received multicast message from %s: %s ", inet_ntoa(SenderAddr.sin_addr), RecvBuf); } } // Leave the multicast group, close the socket, and clean up Winsock setsockopt(RecvSocket, IPPROTO_IP, IP_DROP_MEMBERSHIP, (char*)&Mreq, sizeof(Mreq)); closesocket(RecvSocket); WSACleanup(); return 0; }