c++ - UDP 套接字 revfrom() 返回错误

Question

目的:我的代码是创建一个套接字并从客户端接收一个包(这个客户端每 500 毫秒广播一次消息)。现象:当套接字被创建为主机套接字时，直接使用 revfrom() 将从 revfrom 函数返回 -1。但是，如果我对任何数据包使用 sendto() 函数，则立即使用 revfrom()。这将有助于找到我需要的数据包。用谷歌搜索，它看起来像一个客户端套接字，但我将它创建为服务器套接字。下面是我的代码，有什么建议请指教，不胜感激!代码:

SOCKET s;
sockaddr_in addrDest;
sockaddr_in addrLocal;
int result;
char udp_buff[AMP_MAX_PACKET_SIZE];

WSADATA wsaData;
wchar_t msgbuf[100];

int addrDestSize = sizeof(SOCKADDR_IN);

// initialize winsock
result = WSAStartup(MAKEWORD(2, 2), &wsaData);
if (result != NO_ERROR) {
    wprintf(L"WSAStartup failed with error: %d\n", result);
    //return 1;
}

// create the socket
s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); // UDP socket

u_long iMode = 1;
result = ioctlsocket(s, FIONBIO, &iMode);
if (result != NO_ERROR)
    printf("ioctlsocket failed with error: %ld\n", result);

addrLocal.sin_family = AF_INET;
addrLocal.sin_port = htons(16717);
addrLocal.sin_addr.s_addr = htonl(INADDR_ANY); // zero-init sin_addr to tell it to use all available adapters on the local host

                                               // associate this socket with local UDP port 16717
result = bind(s, (struct sockaddr*)&addrLocal, sizeof(addrLocal));

addrDest.sin_family = AF_INET;
addrDest.sin_port = htons(16717);
inet_pton(AF_INET, "192.168.99.255", &(addrDest.sin_addr));

uint8_t  node_address_temp[6] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };     //array 
std::vector<uint8_t> node_address(node_address_temp, node_address_temp + sizeof(node_address_temp) / sizeof(uint8_t));
//formatDataPack("MID", dataPack, node_address);
//SendCMDToGauge(&s, &dataPack, &addrDest);
result = sendto(s, " ", strlen(" ") + 1, 0, (SOCKADDR *)&addrDest, sizeof(addrDest));

result = -1;
while (result < 0 ) {
    result = recvfrom(s, (char*)&udp_buff, sizeof(udp_buff), 0, (SOCKADDR *)&addrDest, &addrDestSize);
    //result = recv(s, (char*)&udp_buff, sizeof(udp_buff), 0);
    swprintf(msgbuf, 100, L"Revfrom Result: %d\n", result);
    OutputDebugString(msgbuf);
    Sleep(500);
    if (result = 36)
        result = -1;
}

Answer 1

您看到的行为是预期的。您已将套接字设置为非阻塞。因此，如果您调用 recvfrom 并且此时没有任何可接收的内容，它将返回 -1 而不是阻塞。