What this function sendto() does?

Sending to a Named Socket - sendto()

int sendto(int s, char *msg, int len, int flags, struct sockaddr *to, int tolen)

This function allows a message msg of length len to be sent on a socket with descriptor s to the socket named by to and tolen, where tolen is the actual length of to. flags will always be zero for our purposes. The number of characters sent is the return value of the function. On error, -1 is returned and errno describes the error.

An example:

struct sockaddr to_name;

to_name.sa_family = AF_UNIX;
strcpy(to_name.sa_data, "/tmp/sock");

if (sendto(s, buf, sizeof(buf),
0, &to_name,
strlen(to_name.sa_data) +
sizeof(to_name.sa_family)) < 0) {
printf("send failuren");
exit(1);
}