在运行X窗口程序时未获得任何输出

Question

#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/Xos.h>


Display *dis;
int screen;
Window win;
GC gc;
void init_x() {
    /* get the colors black and white (see section for details) */
    unsigned long black,white;

    /* use the information from the environment variable DISPLAY 
       to create the X connection:
    */  
    dis=XOpenDisplay((char *)0);
    screen=DefaultScreen(dis);
    black=BlackPixel(dis,screen),   /* get color black */
    white=WhitePixel(dis, screen);  /* get color white */

    /* once the display is initialized, create the window.
       This window will be have be 200 pixels across and 300 down.
       It will have the foreground white and background black
    */
    win=XCreateSimpleWindow(dis,DefaultRootWindow(dis),0,0, 
        200, 300, 5, white, black);

    /* here is where some properties of the window can be set.
       The third and fourth items indicate the name which appears
       at the top of the window and the name of the minimized window
       respectively.
    */
    XSetStandardProperties(dis,win,"My Window","HI!",None,NULL,0,NULL);

    /* this routine determines which types of input are allowed in
       the input.  see the appropriate section for details...
    */
    XSelectInput(dis, win, ExposureMask|ButtonPressMask|KeyPressMask);

    /* create the Graphics Context */
        gc=XCreateGC(dis, win, 0,0);        

    /* here is another routine to set the foreground and background
       colors _currently_ in use in the window.
    */
    XSetBackground(dis,gc,white);
    XSetForeground(dis,gc,black);

    /* clear the window and bring it on top of the other windows */
    XClearWindow(dis, win);
    XMapRaised(dis, win);
}

int main()
{

init_x();

return 0;
}

This is my first program to get started with X programming. I got this sample code from Internet, I compiled and ran the code but there is no output window.Can anyone please guide me what modification is required here to display a window.

Answer 1

You don't have an event loop, so the program initializes the window and then exits immediately.

Try using

XEvent e;
while (1) {
  XNextEvent(dis, &e);
  if (e.type == KeyPress)
     break;
}

and also clean up on exit using

XCloseDisplay(dis);