XLookupColor() -> X11 RGB colour value example

xlookupcolour.c

/* Paul Sladen, 2014-08-13, Public Domain                                                                                                       
   XLookupColor() -> RGB colour value example, per request on                                                                                   
   http://irclogs.ubuntu.com/2014/08/13/%23ubuntu-devel.html#t19:52                                                                             
   grep MistyRose /usr/share/X11/rgb.txt | awk '{printf("%02x%02x%02x\n",$1,$2,$3);}'                                                           
   http://manpages.ubuntu.com/manpages/man3/XQueryColor.3.html                                                                                  
   gcc xlookupcolour.c -o xlookupcolour -lX11 && ./xlookupcolour red yellow blue                                                                
 */

#include <stdio.h>
#include <X11/Xlib.h>

void main(int argc, char **argv)
{
  Display *dpy;
  Colormap map;
  int scr;
  XColor rgb, nearest_rgb;
  const char *fallback_colours[] = {"red", "white", "blue", "pink", NULL};
  dpy = XOpenDisplay(NULL);
  scr = XDefaultScreen(dpy);
  map = XDefaultColormap(dpy, scr);
  if (argc < 2)
    argv = (char**)fallback_colours;
  for (argv++; *argv; argv++)
    {
      XLookupColor(dpy, map, argv[0], &rgb, &nearest_rgb);
      printf("%3d %3d %3d %s\n", rgb.red>>8, rgb.green>>8, rgb.blue>>8, argv[0]);
    }
}