UDP组播的原理及VC++ 多线程实现发送，接收的程序代码

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。

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\n", retVal);
        return 1;
    }

    // Create a socket for sending data
    SOCKET SendSocket;
    SendSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (SendSocket == INVALID_SOCKET) {
        printf("socket failed: %ld\n", WSAGetLastError());
        WSACleanup();
        return 1;
    }

    // Set the TTL value for the outgoing packets
    int TTL = 2;
    retVal = setsockopt(SendSocket, IPPROTO_IP, IP_MULTICAST_TTL, (char*)&TTL, sizeof(TTL));
    if (retVal == SOCKET_ERROR) {
        printf("setsockopt failed: %d\n", WSAGetLastError());
        closesocket(SendSocket);
        WSACleanup();
        return 1;
    }

    // Set up the destination address 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\n", 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\n", WSAGetLastError());
        return 1;
    }

    return 0;
}

接收端代码：

#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\n", 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\n", 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\n", 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.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\n", 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\n", WSAGetLastError());
            break;
        }
        else {
            RecvBuf[NumBytes] = '\0';
            printf("Received multicast message from %s: %s\n", 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;
}