Sending UDP socket in linux - C language - c

Question

I know that this is obviously elementary question and I know that there are many tutorials and ready-to-go examples but I must missing something. I am trying to send for example text (char *) via UDP socket to other machine in local network. So far I tried some tutorials like http://gafferongames.com/networking-for-game-programmers/sending-and-receiving-packets/ and so on but I always get error in bind() function with errno "Cannot assign requested address".
I just have some data in char array and I want to push them via network to another host. Could someone please point me to the right direction? Do I need socket server or client? Do I need to bind the socket to some interface?
This is my playground:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <errno.h>
int handle;
int init_socket()
{
handle = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (handle <= 0)
{
printf("failed to create socket\n");
return 1;
}
printf("sockets successfully initialized\n");
return 0;
}
int main ()
{
unsigned short port = 30000;
char * data = "hovno";
init_socket();
struct sockaddr_in address;
memset((char *) &address, 0, sizeof(address));
address.sin_family = AF_INET;
address.sin_addr.s_addr = inet_addr("192.168.11.129"); // this is address of host which I want to send the socket
address.sin_port = htons(port);
printf("handle: %d\n", handle); // prints number greater than 0 so I assume handle is initialized properly
if (bind(handle, (const struct sockaddr*) &address, sizeof(struct sockaddr_in)) < 0)
{
printf("failed to bind socket (%s)\n", strerror(errno)); // Cannot assign requested address
return 1;
}
int nonBlocking = 1;
if (fcntl(handle, F_SETFL, O_NONBLOCK, nonBlocking) == -1)
{
printf("failed to set non-blocking\n");
return 2;
}
int sent_bytes = sendto(handle, data, strlen(data), 0, (const struct sockaddr*) &address, sizeof(struct sockaddr_in));
if (sent_bytes != strlen(data))
{
printf("failed to send packet\n");
return 3;
}
return 0;
}

Answer 1

bind is called for the local address (one you intend to recv packets to). The IP address must be a local IP address of the machine, or (most frequently) INADDR_ANY.
Normally you don't have to use bind on the client side at all. The system will pick a suitable free port for you automatically.
To specify the remote address for a UDP socket, use sendto, not send.
If you search Google for udp client c code, one of the first results is this one. You can see that the networking part is basically just two calls, socket and sendto.