udp socket programming in windows

Question

Hi, I developed code to receive udp packets from the port. But after calling recvfrom() nothing is happening. Following is my code and output. Please help. Thanks in advance....

#include "udpSocket.h"

int main(void)
{
 SOCKET sockID;
 WSADATA wsaData = {0};
 FILE *udp;

 char buf[512];

 static int recvData;
    int iResult = 0;
 int sock_len = sizeof(fepAddr);
 int recvResult;
 int seqNo = 0;
 static int outOfSeqCnt = 0;

 FILE *fp = fopen("outOfSeq.txt","a");

 if((udp = fopen("udpData.txt","w")) == 0)
  printf("udpData.txt not opened\n");

 printf("\n-------------------------------------\n");
    printf("\tUDP Packet Receiver\n");
    printf("-------------------------------------\n");

    printf("\n Enter Destination FEP IP Address : ");
    scanf_s("%s",inputData.destIPAddr,16);

    printf("\n Enter Destination port from which to receive data : "); 
    scanf_s("%d",&inputData.portNo,5);

 printf("\n Enter No.of iterations : "); 
    scanf_s("%d",&inputData.noIteration,2);

    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
 if(iResult < 0)
 {
  printf("windows socket startup error\n");
 } 

 sockID = socket(PF_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);
 fepAddr.sin_addr.s_addr = htonl(INADDR_ANY);

 if(bind(sockID, (struct sockaddr *)&fepAddr, sizeof(struct sockaddr)) < 0)
 {
  printf("bind() failed: %ld.\n", WSAGetLastError());
  closesocket(sockID);
  return 0;
 }

 else
 {
  printf("bind() is OK!\n");
 }

 memset(udpBuf, 0, sizeof(udpBuf));

 recvData = 1;

 while (recvData)
 {
  printf("receiving data\n");
  recvResult =  recvfrom(sockID, udpBuf, sizeof(udpBuf), 0,(struct sockaddr *)&fepAddr, &sock_len); 

  if (recvResult <= 0) {
   printf("Socket receive()-error\n");
   goto exit;
  }
  else
   printf("Sock success\n");

  printf("completed rx data\n");

  //puts(udpBuf);
  fprintf(udp, "%s", udpBuf);
  //fwrite(udpBuf, sizeof(udpBuf), 1, udp);

    }

 inputData.noIteration--;
 if (inputData.noIteration <= 0)*/
  recvData-- ;


 }

exit:
    if(udp) 
    {
         fclose(udp);
         udp = 0; 
    }

    //shutdown socket
    closesocket(sockID); 
 fclose(udp);

 return 0;
}

- output::::

---

UDP Packet Receiver

Enter Destination FEP IP Address : 192.168.13.25

Enter Destination port from which to receive data : 2013

Enter No.of iterations : 0 Socket Created bind() is OK! receiving data

Answer 1

Well, first off your bind call should use sizeof(fepAddr) (which I assume is struct sockaddr_in) instead of sizeof(struct sockaddr) to give it a chance of actually binding to the correct address.

Second, are you sure that someone is actually sending you data? otherwise recvfrom will block by default.