Handle C-q with XLookupString - c

Question

This is a working example of X11 code that handles Ctrl-q event to quit application:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/Xos.h>
void exitOnCondition(char cond, const char *msg, int exitCode, Display *dpy, Window *w, GC *gc) {
if(cond) {
printf("%s\n", msg);
if(dpy && gc) XFreeGC(dpy, *gc);
if(dpy && w) XDestroyWindow(dpy, *w);
if(dpy) XCloseDisplay(dpy);
exit(exitCode);
}
}
int main(int argc, char **argv) {
Display *dpy = XOpenDisplay(0);
exitOnCondition(dpy == 0, "Error: XOpenDisplay failed", -1, dpy, 0, 0);
int blackColor = BlackPixel(dpy, DefaultScreen(dpy));
int whiteColor = WhitePixel(dpy, DefaultScreen(dpy));
Window w = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy), 0, 0,
200, 100, 0, blackColor, blackColor);
//Tell X Server to send MapNotify events
XSelectInput(dpy, w, StructureNotifyMask | KeyPressMask);
//Make window appear
XMapWindow(dpy, w);
//Graphics Context
GC gc = XCreateGC(dpy, w, 0, 0);
//Set white color for drawing
XSetForeground(dpy, gc, whiteColor);
//Wait for the MapNotify event
for(;;) {
XEvent e;
XNextEvent(dpy, &e);
if (e.type == MapNotify) {
break;
}
}
//Draw the line
XDrawLine(dpy, w, gc, 10, 60, 180, 20);
//Send the "DrawLine" request to the server
XFlush(dpy);
char text[255];
XEvent e;
KeySym key;
int numKeys = 0;
for(;;) {
XNextEvent(dpy, &e);
if(e.type == KeyPress) {
//With modifier XLookupString will return garbage(?) in text[0] and key as latin1
if((numKeys = XLookupString(&e.xkey, text, 255, &key, 0))) {
printf("lookup returned:\n");
for(int i = 0; i < numKeys; i++) {
printf("text[%d]=%x\n", i, text[i]);
}
if(e.xkey.state == ControlMask && key == XK_q) {
exitOnCondition(1, "C-Q pressed", 0, dpy, &w, &gc);
}
}
}
}
XFreeGC(dpy, gc);
XDestroyWindow(dpy,w);
XCloseDisplay(dpy);
}
Will this code correctly handle Ctrl-q event on any system?
Can I use e.xkey.state to check for Ctrl modifier after XLookupString for any keyboard layout even when Ctrl is rebound to CAPS Lock(or anything else)?
Why does XLookupString return one symbol text[0]==0x11 for Ctrl-q event and not text[0]==CtrlModifierCode text[1]=='q'?

Answer 1

XLookupString returns a sequence of ISO-8859-1 characters (at least according to the manual I have; I do not know how up-to-date it is). There is no character code in ISO-8859-1 for the "ctrl" key by itself. Strictly speaking, there isn't one for the ctrl-q combination either, but tradition dictates that ctrl + (A...Z) map to the 1...26 range.