Hi All,

Below is my code for a non blocking UDP socket, this code compiles fine with g++, however when I run it i get the error NON: recvfrom: Resource temporarily unavailable. Please help with any advice

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <time.h>
#include <string>
#include <stdio.h>
#include <iostream>
#include <map>
#include <unistd.h>
#include <fcntl.h>

using namespace std;

int main(int argc, char *argv[])
{

struct sockaddr_in addr;
int sock, nbytes,addrlen, flags;
struct ip_mreq mreq;
char msgbuf[1024];

int yes = 1;


if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
{
perror("socket");
exit(1);
}

flags = fcntl(sock,F_GETFL);
flags |= O_NONBLOCK;


// allow multiple sockets to use the same PORT number
if ( (setsockopt (sock, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof( yes )) < 0))
{
perror("Reusing ADDR failed");
exit(1);
}

// setting up destination addres
memset(&addr, 0, sizeof( addr ));
addr.sin_family=AF_INET;
addr.sin_addr.s_addr=inet_addr(SOCK_GROUP);
addr.sin_port=htons(SOCK_PORT);

// bind to receive address
if (bind (sock, (struct sockaddr *) &addr, sizeof( addr )) < 0)
{
perror("bind");
exit(1);
}

//Join the multicast group
mreq.imr_multiaddr.s_addr=inet_addr(SOCK_GROUP);
mreq.imr_interface.s_addr=htonl(INADDR_ANY);
if (setsockopt (sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof( mreq )) < 0)
{
perror("setsockopt");
exit(1);
}


fcntl(sock, F_SETFL, flags);

// now just enter a read-print loop
while(1) {

addrlen=sizeof(addr);
if ((nbytes = recvfrom(sock, msgbuf, sizeof( msgbuf ), 0, (struct sockaddr *) &addr, (socklen_t*) &addrlen)) < 0)
{
perror("NON: recvfrom");
exit(1);

}//Closes the if
else
{
cout <<" got something "<<endl;
}
}
};

My guess is that there's nothing to read on the socket, and as you configure it as non-blocking, the "recvfrom" return with this error which isn't a real one...

2 remarks:
1°) Use "code" take to make your code more readable
2°) It looks like you're mixing C and C++, don't do that

Since you are using non-blocking sockets, you would need to compare the errno against -EAGAIN to make sure that you can go back to sleep till there is something to receive. You can use select()/poll() to see if the socket is ready for data.

man 2 recvfrom