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TCP/IP in c (unix)
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XOpenDisplay() XOpenDisplay() Name XOpenDisplay - connect a client program to an X server. Synopsis Display *XOpenDisplay(display_name) char *display_name; Arguments display_name Specifies the display name, which determines the server to connect to and the communications domain to be used. See Description below. Returns The display structure. Description The XOpenDisplay() routine connects the client to the server controlling the hardware display through TCP or DECnet communication proto- cols, or through some local inter-process communication protocol. On a POSIX-conformant system, if display_name is NULL, the value defaults to the contents of the DISPLAY environment variable on POSIX- based systems. On non-UNIX-based systems, see that operating system's Xlib manual for the default display_name. The encoding and inter- pretation of the display name is implementation-dependent. Strings in the Host Portable Character Encoding are supported; support for other characters is implementation-dependent. The display_name or DISPLAY environment variable is a string that has the format host- name:server or hostname:server.screen. For example, frog:0.2 would specify screen 2 of server 0 on the machine frog. hostname Specifies the name of the host machine on which the display is physically connected. You follow the hostname with either a single colon (:) or a double colon (::), which determines the communications domain to use. Any or all of the communication protocols can be used simultaneously on a server built to support them (but only one per client). o If hostname is a host machine name and a single colon (:) separates the hostname and display number, XOpenDisplay() connects to the server using TCP streams. If the hostname is not specified, Xlib uses what it believes is the fastest transport. o If hostname is a host machine name and a double colon (::) separates the hostname and display number, XOpenDisplay() con- nects with the server using DECnet streams. To use DECnet, however, you must build all software for DECnet. A single X server can accept both TCP and DECnet connections if it has been built for DECnet. o Note that support for use of the string "unix" in a display name is no longer part of the Xlib specification as of Release 4. server Specifies the number of the server on its host machine. This display number may be followed by a period (.). A single CPU can have more than one display; the displays are numbered starting from 0. screen Specifies the number of the default screen on server. Multiple screens can be connected to (controlled by) a single X server, but they are used as a single display by a single user. screen merely sets an internal variable that is returned by the DefaultScreen() macro. If screen is omitted, it defaults to 0. If successful, XOpenDisplay() returns a pointer to a Display. This structure provides many of the specifications of the server and its screens. If XOpenDisplay() does not succeed, it returns NULL. After a successful call to XOpenDisplay(), all of the screens on the server may be used by the application. The screen number specified in the display_name argument serves only to specify the value that will be returned by the DefaultScreen() macro. After opening the display, you can use the ScreenCount() macro to determine how many screens are available. Then you can reference each screen with integer values between 0 and the value returned by (ScreenCount() -1). You can access elements of the Display and Screen structures only using the infor- mation macros and functions listed in Appendix C, Macros. For more information, see Volume One, Chapter 2, X Concepts, and Chapter 3, Basic Window Program. See Also XDefaultScreen(), XCloseDisplay(), XFree(), XNoOp(). Xlib - HouseKeeping XOpenDisplay()
