2.1. Opening the Display
To open a connection to the X server that controls a display, use
XOpenDisplay().
Syntax
Display *XOpenDisplay(display_name)
char *display_name;
Arguments
| display_name
|
Specifies the hardware display name, which determines the display
and communications domain to be used.
On a POSIX-conformant system, if the display_name is NULL,
it defaults to the value of the DISPLAY environment variable.
|
Description
The encoding and interpretation of the display name is
implementation dependent.
Strings in the Host Portable Character Encoding are supported;
support for other characters is implementation dependent.
On POSIX-conformant systems,
the display name or DISPLAY environment variable can be a string in the format:
hostname:number.screen_number
| hostname
| Specifies the name of the host machine on which the display is physically
attached.
You follow the hostname with either a single colon (:) or a double colon (::).
|
| number
| Specifies the number of the display server on that host machine.
You may optionally follow this display number with a period (.).
A single CPU can have more than one display.
Multiple displays are usually numbered starting with zero.
|
| screen_number
| Specifies the screen to be used on that server.
Multiple screens can be controlled by a single X server.
The screen_number sets an internal variable that can be accessed by
using the
DefaultScreen()
macro or the
XDefaultScreen()
function if you are using languages other than C (see "Display Macros").
|
For example, the following would specify screen 1 of display 0 on the
machine named ``dual-headed'':
dual-headed:0.1
The
XOpenDisplay()
function returns a
Display
structure that serves as the
connection to the X server and that contains all the information
about that X server.
XOpenDisplay()
connects your application to the X server through TCP
or DECnet communications protocols,
or through some local inter-process communication protocol.
If the hostname is a host machine name and a single colon (:)
separates the hostname and display number,
XOpenDisplay()
connects using TCP streams.
If the hostname is not specified,
Xlib uses whatever it believes is the fastest transport.
If the hostname is a host machine name and a double colon (::)
separates the hostname and display number,
XOpenDisplay()
connects using DECnet.
A single X server can support any or all of these transport mechanisms
simultaneously.
A particular Xlib implementation can support many more of these transport
mechanisms.
If successful,
XOpenDisplay()
returns a pointer to a
Display
structure,
which is defined in
X11/Xlib.h.
If
XOpenDisplay()
does not succeed, it returns NULL.
After a successful call to
XOpenDisplay()
all of the screens in the display can be used by the client.
The screen number specified in the display_name argument is returned
by the
DefaultScreen()
macro (or the
XDefaultScreen()
function).
You can access elements of the
Display
and
Screen
structures only by using the information macros or functions.
For information about using macros and functions to obtain information from
the
Display
structure,
see Display Macros.
X servers may implement various types of access control mechanisms
(see "Controlling Host Access").
Christophe Tronche, [email protected]
