udp winsock programming - udp

Question

I'm the beginner in socket programming. I want to receive udp packets continuously from the port. For that I created socket and using bind and recv calls I have done with my program. In a buffer I'm storing the udp packets. How to receive packet by packet. How to put condition for particular time interval? Thanks in advance.
static int recvData = 1;
sockID = socket(AF_INET, SOCK_DGRAM, 0);
if(sockID < 0)
{
printf("Socket creation error\n");
WSACleanup();
}
else
{
printf("Socket Created\n");
}
fepAddr.sin_family = AF_INET;
fepAddr.sin_port = htons(inputData.portNo);
fepAddr.sin_addr.s_addr = inet_addr(inputData.destIPAddr);
if (bind(sockID, (struct sockaddr *)&fepAddr, sizeof(fepAddr)) == SOCKET_ERROR)
{
printf("bind() failed: %ld.\n", WSAGetLastError());
closesocket(sockID);
return 0;
}
else
{
printf("bind() is OK!\n");
}
memset(udpBuf,sizeof(udpBuf),0);
while (recvData)
{
printf("receiving data\n");
recvResult = recvfrom( sockID, udpBuf, sizeof(udpBuf), 0,(struct sockaddr *)&fepAddr, &sock_len);
fprintf(udp, "%s", udpBuf);
//fwrite(udpBuf, sizeof(udpBuf), 1, udp);
recvData-- ;
}
exit:
if(udp)
{
fclose(udp);
udp = 0;
}
//shutdown socket
closesocket(sockID);
fclose(udp);

Answer 1

recvfrom() receives UDP data packet-by-packet. If a given packet is too large, recvfrom() will return an error. As for timing, you can use select() to know when the socket is readable.
Try something like this:
sockID = socket(AF_INET, SOCK_DGRAM, 0);
if (sockID == INVALID_SOCKET)
{
printf("Socket creation error\n");
goto exit;
}
printf("Socket Created\n");
memset(&fepAddr, 0, sizeof(fepAddr));
fepAddr.sin_family = AF_INET;
fepAddr.sin_port = htons(inputData.portNo);
fepAddr.sin_addr.s_addr = inet_addr(inputData.destIPAddr);
if (bind(sockID, (struct sockaddr *)&fepAddr, sizeof(fepAddr)) == SOCKET_ERROR)
{
printf("bind() failed: %ld.\n", WSAGetLastError());
goto exit;
}
printf("bind() is OK!\n");
memset(udpBuf, 0, sizeof(udpBuf));
printf("receiving data\n");
while (...)
{
printf(".");
recvResult = recvfrom(sockID, udpBuf, sizeof(udpBuf), 0, (struct sockaddr *)&fepAddr, &addr_len);
if (recvResult == SOCKET_ERROR)
{
if (WSAGetLastError() != WSAEWOULDBLOCK)
{
printf("\nrecvfrom() failed: %ld.\n", WSAGetLastError());
goto exit;
}
fd_set fd;
FD_ZERO(&fd);
FD_SET(sockID, &fd);
timeval t;
t.tv_sec = ...; // seconds
t.tv_usec = ...; // microseconds
selectResult = select(0, &fd, NULL, NULL, &t);
if (selectResult == SOCKET_ERROR)
{
printf("\nselect() failed: %ld.\n", WSAGetLastError());
goto exit;
}
if (selectResult == 0)
{
printf("\nsocket timed out.\n");
goto exit;
}
continue;
}
if (recvResult > 0)
fwrite(udpBuf, recvResult, 1, udp);
}
exit:
if (udp != 0)
{
fclose(udp);
udp = 0;
}
if (sockID != INVALID_SOCKET)
{
closesocket(sockID);
sockID = INVALID_SOCKET;
}