sendto
Prototype:
#include <sys/socket.h>
#include <resolv.h>
int sendto(int sockfd, char* msg, int len, int options,
struct sockaddr *addr, int addr_len);
General Description: Send a message to a specific destination without connecting. Typically, you use this system call for UDP and raw sockets. Using this call for TCP sockets is Transaction TCP (T/TCP). (Linux, however, does not yet support T/TCP.)
Return Value: Returns the number of bytes sent or -1 if an error occurred.
Parameters
sockfd The socket descriptor.
msg The data to send.
len The number of bytes to send.
options Message-controlling flags (same as send()).
addr The address of the destination.
addr_len The size of the destination data body.
Possible Errors
(same as send())
Examples
int sockfd;
struct sockaddr_in addr;
if ( (sd = socket(PF_INET, SOCK_DGRAM, 0)) < 0 )
    perror("socket");
bzero(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(DEST_PORT);
inet_aton(DEST_ADDR, &addr.sin_addr);
if ( send(sockfd, buffer, msg_len, 0, &addr, sizeof(addr)) < 0 )
    perror("sendto");