recvfrom
Prototype: 
#include <sys/socket.h>
#include <resolv.h>
int recvfrom(int sockfd, char *buf, int buf_len, int options,
struct sockaddr *addr, int *addr_len);
General Description: Wait for and receive a message from an unconnected peer (UDP and raw sockets). Please note that T/TCP never uses this call. Instead, the receiver uses accept() like usual.
Return Value: If successful, the number of bytes read. If an error occurred, the return value is -1, and errno holds the error code.
Parameters
sockfd The open socket descriptor.
buf The byte array to receive the data.
buf_len The maximum size of the buffer (message truncated and dropped if buffer too small).
options Channel controlling options (same as recv()).
addr The sending peer's address and port.
addr_len The maximum size of addr (address truncated if too small). Upon return, this value changes to match the number of bytes used.
Possible Errors
(same as recv())
Examples 
struct sockaddr_in addr;
int addr_len=sizeof(addr), bytes_read;
char buf[1024];
int sockfd = socket(PF_INET, SOCK_DGRAM, 0);

bytes_read = recvfrom(sockfd, buf, sizeof(buf), 0, &addr, &add_len);
if ( bytes_read < 0 )
    perror("recvfrom failed");