Provided by: libx11-doc_1.6.4-3ubuntu0.4_all 
NAME
XOpenDisplay, XCloseDisplay - connect or disconnect to X server
SYNTAX
Display *XOpenDisplay(char *display_name);
int XCloseDisplay(Display *display);
ARGUMENTS
display Specifies the connection to the X server.
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 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
section 2.2.1.
The XCloseDisplay function closes the connection to the X server for the display specified in the Display
structure and destroys all windows, resource IDs (Window, Font, Pixmap, Colormap, Cursor, and GContext),
or other resources that the client has created on this display, unless the close-down mode of the
resource has been changed (see XSetCloseDownMode). Therefore, these windows, resource IDs, and other
resources should never be referenced again or an error will be generated. Before exiting, you should
call XCloseDisplay explicitly so that any pending errors are reported as XCloseDisplay performs a final
XSync operation.
XCloseDisplay can generate a BadGC error.
SEE ALSO
AllPlanes(3), XFlush(3), XSetCloseDownMode(3) Xlib - C Language X Interface