网络协议--UDP协议（4）组播

组播就是将数据发送到一组主机。接收端如果要接收消息，则需要加入到该分组，分组是用IP来标识的。
从网络协议–UDP协议（1）介绍可以知道，适用于分组的IP有224.0.0.0 ~ 239.255.255.255。
同样，发送端就需要将数据发送到该分组IP。

一、发送端

#include 
#pragma comment(lib, "Ws2_32.lib")


void SendLogic() {
    WSADATA wsaData;
    WORD wVersiOnRequested= MAKEWORD(1, 0);
    WSAStartup(wVersionRequested, &wsaData);

    SOCKET socket = ::WSASocket(AF_INET, SOCK_DGRAM, IPPROTO_UDP, nullptr, 0, 0);
    if (socket == INVALID_SOCKET) {
        printf("WSASocket failed, error=%d\n", WSAGetLastError());
        return;
    }

    // 将套接字配置为发送广播消息
    int broadcast = 1;
    int err = setsockopt(socket, SOL_SOCKET, SO_BROADCAST, reinterpret_cast<const char*>(&broadcast), sizeof(int));
    if (err == SOCKET_ERROR) {
        printf("setsockopt failed, error=%d\n", WSAGetLastError());
        return;
    }

    sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(6000);
    addr.sin_addr.s_addr = inet_addr("225.0.0.37"); // 向指定广播组发送消息

    char buf[100] = { "hello" };
    err = sendto(socket, buf, strlen(buf), 0, reinterpret_cast<const sockaddr*>(&addr), sizeof(addr));
    if (err == SOCKET_ERROR) {
        printf("sendto failed, error=%d\n", WSAGetLastError());
        return;
    }

    printf("[BROADCAST] %s OK\n", buf);

    WSACleanup();
}

int main()
{
    SendLogic();

    getchar();
    return 0;
}

二、接收端

#include 
#include 


#pragma comment(lib, "Ws2_32.lib")

void RecvLogic() {
    WSADATA wsaData;
    WORD wVersiOnRequested= MAKEWORD(1, 0);
    WSAStartup(wVersionRequested, &wsaData);

    SOCKET socket = ::WSASocket(AF_INET, SOCK_DGRAM, IPPROTO_UDP, nullptr, 0, 0);
    if (socket == INVALID_SOCKET) {
        printf("WSASocket failed, error=%d\n", WSAGetLastError());
        return;
    }

    sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons(6000);
    addr.sin_addr.s_addr = htonl(INADDR_ANY);

    int err = bind(socket, reinterpret_cast<const sockaddr*>(&addr), sizeof(addr));
    if (err == SOCKET_ERROR) {
        printf("bind failed, error=%d\n", WSAGetLastError());
        return;
    }

    // 将SOCKET加入广播组
    //
    struct ip_mreq mreq; // 引入头文件
    mreq.imr_multiaddr.s_addr = inet_addr("225.0.0.37");  // 广播组地址
    mreq.imr_interface.s_addr = htonl(INADDR_ANY);

    // 注：使用IP_DROP_MEMBERSHIP可以离开广播组
    err = setsockopt(socket, IPPROTO_IP, IP_ADD_MEMBERSHIP, reinterpret_cast<const char*>(&mreq), sizeof(ip_mreq));
    if (err == SOCKET_ERROR) {
        printf("setsockopt failed, error=%d\n", WSAGetLastError());
        return;
    }

    while (true) {
        char buf[100] = { 0 };
        int fromlen = sizeof(addr);
        err = recvfrom(socket, buf, 100, 0, reinterpret_cast(&addr), &fromlen);
        if (err == SOCKET_ERROR) {
            printf("recvfrom failed, error=%d\n", WSAGetLastError());
            return;
        }

        printf("[RECV] %s\n", buf);
    }

    WSACleanup();
}

int main()
{
    RecvLogic();

    getchar();
    return 0;
}