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<HTML><HEAD><TITLE>Xlib Programming Manual: Display: opening (XOpenDisplay)</TITLE></HEAD><BODY><H1 ALIGN=center>2.1. Opening the Display</H1>To open a connection to the X server that controls a display, use<B>XOpenDisplay()</B>.<H2>Syntax</H2><!.IN "XOpenDisplay" "" "@DEF@"><PRE><CODE>Display *XOpenDisplay(<B>display_name</B>) char *<B>display_name</B>;</CODE></PRE><H2>Arguments</H2><TABLE><TR><TD><B>display_name</B><TD>Specifies the hardware display name, which determines the displayand 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. <!.IN "Environment" "DISPLAY"></TABLE><H2>Description</H2>The encoding and interpretation of the display name isimplementation 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:<P><CODE><PRE><I> hostname:number.screen_number</I></PRE></CODE><P><TABLE><TR><TD> <B>hostname</B><TD> Specifies the name of the host machine on which the display is physicallyattached.You follow the hostname with either a single colon (:) or a double colon (::).<TR><TD> <B>number</B><TD> 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.<!.IN "Screen"><TR><TD> <B>screen_number</B><TD> 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 byusing the <B><A HREF="display-macros.html#DefaultScreen">DefaultScreen()</A></B>macro or the <B><A HREF="display-macros.html#DefaultScreen">XDefaultScreen()</A></B>function if you are using languages other than C (see "<A HREF="information.html#display">Display Macros</A>").</TABLE><P>For example, the following would specify screen 1 of display 0 on the machine named ``dual-headed'':<P><BLOCKQUOTE>dual-headed:0.1</BLOCKQUOTE><P>The<B>XOpenDisplay()</B>function returns a <A HREF="#Display">Display</A> structure that serves as theconnection to the X server and that contains all the informationabout that X server.<B>XOpenDisplay()</B>connects your application to the X server through TCP or DECnet communications protocols,or through some local inter-process communication protocol.<!.IN "Protocol" "TCP"><!.IN "Protocol" "DECnet">If the hostname is a host machine name and a single colon (:)separates the hostname and display number,<B>XOpenDisplay()</B>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,<B>XOpenDisplay()</B>connects using DECnet.A single X server can support any or all of these transport mechanismssimultaneously.A particular Xlib implementation can support many more of these transportmechanisms.<P><!.IN "Display"><A NAME="Display"></A>If successful, <B>XOpenDisplay()</B> returns a pointer to a <B>Display</B> structure,which is defined in <B>X11/Xlib.h</B>.If <B>XOpenDisplay()</B> does not succeed, it returns NULL.After a successful call to<B>XOpenDisplay()</B> 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 <B><A HREF="display-macros.html#DefaultScreen">DefaultScreen()</A></B>macro (or the<B><A HREF="display-macros.html#DefaultScreen">XDefaultScreen()</A></B>function).You can access elements of the<B>Display</B>and<A HREF="display-macros.html">Screen</A>structures only by using the information macros or functions.For information about using macros and functions to obtain information from the<B>Display</B> structure,see <A HREF="information.html#display">Display Macros</A>.<P>X servers may implement various types of access control mechanisms(see "<A HREF="../window-and-session-manager/controlling-host-access/">Controlling Host Access</A>").<H5 ALIGN=right><I>Next: <A HREF="information.html">Obtaining Information about the Display, Image Formats, or Screens</A></I></H5><HR><ADDRESS><A HREF="http://tronche.com/">Christophe Tronche</A>, <A HREF="mailto:ch.tronche@computer.org">ch.tronche@computer.org</A></ADDRESS></BODY></HTML>⌨️ 快捷键说明
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