Page:Xlib - C Language X Interface.pdf/14

 {| style="background:#F0F0F0; color: #202122;" cellpadding=10px colon. more than one display. Multiple displays are usually numbered starting with zero.
 * ||protocol/hostname:number.screen_number
 * - valign=top
 * protocol || Specifies a protocol family or an alias for a protocol family. Supported protocol families are implementation dependent. The protocol entry is optional. If protocol is not specified, the / separating protocol and hostname must also not be specified.
 * - valign=top
 * 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
 * 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
 * - valign=top
 * 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
 * - valign=top
 * 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 section 2.2.1).
 * }

For example, the following would specify screen 1 of display 0 on the machine named "dualheaded":


 * 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 protocol is specified as "tcp", "inet", or "inet6", or if no protocol is specified and the hostname is a host machine name and a single colon separates the hostname and display number, XOpenDisplay connects using TCP streams. (If the protocol is specified as "inet", TCP over IPv4 is used. If the protocol is specified as "inet6", TCP over IPv6 is used. Otherwise, the implementation determines which IP version is used.) If the hostname and protocol are both 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 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.

X servers may implement various types of access control mechanisms (see section 9.8).