BSD Sockets Interface Programmer's Guide

Chapter 4 95

Using Internet Datagram Sockets

Sending and Receiving Messages

The sendto and recvfrom (or sendmsg and recvmsg) system calls are

usually used to transmit and receive messages.

Sending Messages

Use sendto or sendmsg to send messages. sendmsg allows the send

data to be gathered from several buffers.

If you have declared a default address, you can use send , sendto, or

sendmsg to send messages. If you use sendto or sendmsg in this special

case, be sure you specify 0 as the address value or an error will occur.

send is described in the “Sending Data” section in the “BSD Sockets:

Using Internet Stream Sockets” chapter of this guide and in the

send(2) man page. sendto and its parameters are described in the

following table.

Include ﬁles: #include <sys/types.h>

#include <netinet/in.h>

#include <sys/socket.h>

System call: count = sendto(s,msg,len,flags,to,tolen) int s

char *msg;

int len, flags;

struct sockaddr *to

int tolen;

Parameter Description of Contents INPUT Value

s socket descriptor of local

socket

socket descriptor of

socket sending message

msg pointer to data buffer pointer to data to be

sent

len size of data buffer size of msg