How to react to mouse wheel in Xlib? - c

Question

I want to execute code when user will use mouse wheel. I wrote simple example application and it is not working. Why my application is not reacting on mouse wheel?
#include <X11/Xlib.h>
#include <X11/X.h>
#include <X11/Xutil.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void) {
Display *d;
Window w;
XEvent e;
char *msg = "Hello, World!";
int s;
d = XOpenDisplay(NULL);
if (d == NULL) {
fprintf(stderr, "Cannot open display\n");
exit(1);
}
s = DefaultScreen(d);
w = XCreateSimpleWindow(d, RootWindow(d, s), 10, 10, 100, 100, 1,
BlackPixel(d, s), WhitePixel(d, s));
XSelectInput(d, w, ExposureMask | ButtonPressMask);
XMapWindow(d, w);
while (1) {
XNextEvent(d, &e);
if (e.type == Expose) {
XFillRectangle(d, w, DefaultGC(d, s), 20, 20, 10, 10);
XDrawString(d, w, DefaultGC(d, s), 10, 50, msg, strlen(msg));
}
if (e.type == ButtonPress){
switch (e.xbutton.button){
case Button4:
printf("Scrolled up");
break;
case Button5:
printf("Scrolled down");
break;
default:
printf("cos");
}
}
}
XCloseDisplay(d);
return 0;
}

Answer 1

your code is correct, the reason you don't see results immediately is because fprintf buffers data until newline. Replace your debug lines with something like printf("Scrolled up\n"); and you'll see results immediately. Alternatively you might do setbuf(stdout, NULL); to disable buffering.
See this related SO question: Why does printf not flush after the call unless a newline is in the format string?