CODEWITHSUNDEEP
csockets
Shreyas Kale
Shreyas Kale

Reputation: 65

Implementing UDP sockets with select in C

I am implementing a socket programming project in C. I am using select() for waiting for data from client. I have two UDP sockets and select() is always ignoring one of my sockets.

Can anybody briefly describe where should I start looking for it? This is what my server is doing

waitThreshold.tv_sec = 5000; 
waitThreshold.tv_usec = 50; 
if (sd > sd1)
    max_sd = (sd + 1);
else if(sd1 > sd)   
    max_sd = (sd1 + 1);
FD_ZERO(&read_sds); 
FD_SET(sd, &read_sds); 
FD_SET(sd1, &read_sds);   

ret = select(max_sd, &read_sds, NULL, NULL, &waitThreshold); 
if (ret < 0) {
    printf("\nSelect thrown an exception\n");   
    return 0;
} else if (FD_ISSET(sd, &read_sds)) { 
    // code for socket one 
} else if (FD_ISSET(sd1, &read_sds)) {
    // code for socket two 
}

Upvotes: 1

Views: 19418

Answers (1)

suraj_fale
suraj_fale

Reputation: 960

You must set and reset after each iteration

if(sd > sd1)    
      max_sd = (sd + 1);
else if(sd1 > sd)   
      max_sd = (sd1 + 1);
//some code
while(1){
   waitThreshold.tv_sec = 5000; 
   waitThreshold.tv_usec = 50;    
   FD_ZERO(&read_sds); 
   FD_SET(sd, &read_sds); 
   FD_SET(sd1, &read_sds);
   ret = select(max_sd, &read_sds, NULL, NULL, &waitThreshold); 
   if(ret <0)
   { 
     printf("\nSelect thrown an exception\n");   
     return 0;
   } 
   else if(FD_ISSET(sd, &read_sds)) 
    { // code for socket one }  
   else if(FD_ISSET(sd1, &read_sds)) 
   { // code for socket two }</pre></code>
}

Now it will solve your problem.

Upvotes: 2

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