HP X.25/9000 Programmer's Guide

52 Chapter4

Sending and Receiving Data

Data Transmission Requirements

sd Socket descriptor for a connected VC socket.

msg Pointer to the buffer containing the data to be transmitted over the VC.

Although this is a character buffer, X.25 has no requirement that the

data actually be ASCII characters. This is entirely up to the application.

len Length of the

msg

buffer in bytes.

ﬂags Indicates the type of data and packet in which to send the data. If 0 is

speciﬁed, then X.25 sends a DATA packet containing the data. If the

out-of- band ﬂag is set (OOB_MSG), then X.25 sends an INTERRUPT

packet containing the data. For details on sending interrupt data, refer

to Chapter 5 , “Receiving and Transmitting Out-of-band Information.”

count Returned value is either –1 or the number of bytes actually sent. If

count

is –1, then

errno

contains the error code. If

errno

returned

EINTR, a signal was received.

If a SIGURG signal is received during a send() call, the state of the VC

may have changed. Design your program to check the state of the VC

before attempting to send() data again after a SIGURG signal has

arrived.

Refer to the send(2) entry in your HP-UX man pages for more

information.

Receiving Data

The recv(2) and read(2) calls can be issued any time after a connection

has been established. The caller is blocked until there is a message

available for reception, unless nonblocking I/O is being used.

Nonblocking I/O is described later in this chapter. Refer also to “Sending

and receiving large messages” later in this section for information on

how large messages are sent and received.

Syntax for recv()

The syntax for the recv() system call and its parameters are described

below. The syntax for read() is described in your HP-UX man pages.

#include <sys/types.h>

#include <sys/socket.h>

int count;

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