XOpenDisplay, XCloseDisplay − connect or disconnect to X

Display *XOpenDisplay(char *display_name); int
XCloseDisplay(Display *display);

display   Specifies the connection to the X server.

          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.

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 If XOpenDisplay does not
succeed, it returns NULL.  After a successful call to 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 and or other
resources that the client has created on this display,
unless the close‐down mode of the resource has been changed
(see 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.

AllPlanes(3), XFlush(3), XSetCloseDownMode(3)
Xlib − C Language X Interface