My code doesn't receive a message from xserver - linux

Question

I want to receive a message from xserver when I close my window.
(when I hit the 'X' button')
For example, I have a list of windows that are currently opened. (can be referred by dayRecord.)
I want to print that "window closed!" when I click the x button on a terminal.
But though I clicked it, I couldn't get any message from xserver.
Also, that XNextEvent is blocking.
I've test this exact same logic with a window generated in my code using XCreateSimpleWindow,
and it worked perfectly.
I can even close an existing window I created manualy by XDestroyWindow.
So, I think there is no difference between a window that is created by the code
and created before the code starts once if I have a window id.
But somehow, I cannot get any message from a former one.
This is my code.
It is trying to get a list of windows that are opened.
And within them, when I close a terminal it should print "window closed!"
void windowManager() {
// getting a text viewer to be traced
char **textViewers = getTextViewers();
// retreiving new record of a day
DayRecord *dayRecord = getNewDayRecord();
// save an x11 display, and currently opened windows into the day record
Display *display = recordInit(dayRecord);
Window whatToClose;
for (int i = 0; i < dayRecord->recordCnt; ++i) {
printf("currently opened: %s %lu\n", dayRecord->record[i].name, dayRecord->record[i].window);
// for example: i want to know when a terminal is closed. (before the program starts, it should be opened, or it crashes.)
if (strcmp(dayRecord->record[i].name, "gnome-terminal-server") == 0)
whatToClose = dayRecord->record[i].window;
addInfoSpace(display, dayRecord->record + i, textViewers);
}
printf("let's close %lu: %s\n", whatToClose, getWindowName(display, whatToClose));
// window close detecting logic down here...
Atom wmDelete = XInternAtom(display, "WM_DELETE_WINDOW", False);
XSetWMProtocols(display, whatToClose, &wmDelete, 1);
XEvent xEvent;
printf("I am listening!\n");
while (True) {
XNextEvent(display, &xEvent);
if (xEvent.type == ClientMessage && xEvent.xclient.data.l[0] == wmDelete) {
printf("window closed!\n");
break;
}
}
char *json = (char *)malloc(sizeof(char) * 100000);
dayRecordToJSON(dayRecord, json);
printf("%s", json);
// freeing memories
free2dArray((void **)textViewers, MAX_FILE_COUNT);
freeDayRecord(dayRecord);
XCloseDisplay(display);
}
Thank you.

Answer 1

I've tried many things and this worked.
If you're trying to do the same thing, please check the code.
But, I am not sure if this is a right way to do.
Maybe there can be a safer and right way to do this but this works anyway.
// ...
Atom wmDelete = XInternAtom(display, "WM_DELETE_WINDOW", False);
XSetWMProtocols(display, whatToClose, &wmDelete, 1);
XSelectInput(display, whatToClose, SubstructureNotifyMask);
XEvent xEvent;
printf("I am listening!\n");
while (1) {
XNextEvent(display, &xEvent);
if (xEvent.type == DestroyNotify) {
printf("window closed!\n");
break;
}
}
// ...