Get window title with XCB - c++

Question

I am trying to get information about the window in focus. It seems that I get a correct window id from xcb_get_input_focus_reply_t->focus: it stays the same for my Eclipse IDE (56623164) and is another for any other window in focus. However, the value length is always 0 for XCB_ATOM_WM_NAME.
shortened code
cookie = xcb_get_property(c, 0, fr->focus, XCB_ATOM_WM_NAME,
XCB_ATOM_STRING, 0, 0);
if ((reply = xcb_get_property_reply(c, cookie, NULL))) {
int len = xcb_get_property_value_length(reply);
if (len == 0) {
printf("Zero Length\n");
free(reply);
return;
}
printf("WM_NAME is %.*s\n", len, (char*) xcb_get_property_value(reply));
}
Eclipse Debugger
reply xcb_get_property_reply_t * 0x60bd40
response_type uint8_t 1 '\001'
format uint8_t 0 '\0'
sequence uint16_t 2
length uint32_t 0
type xcb_atom_t 0
bytes_after uint32_t 0
value_len uint32_t 0
pad0 unsigned char [12] 0x60bd54
There is no error (I passed and inspected a xcb_generic_error_t). Do you have any idea what could go wrong? Maybe I should use Xlib instead...

Answer 1

This code works for me, it is in js-ctypes but you can ignore that part and see this for API use:
var win = aXcbWindowT;
// console.log('win:', win);
var req_title = ostypes.API('xcb_get_property')(ostypes.HELPER.cachedXCBConn(), 0, win, ostypes.CONST.XCB_ATOM_WM_NAME, ostypes.CONST.XCB_ATOM_STRING, 0, 100); // `100` means it will get 100*4 so 400 bytes, so that 400 char, so `rez_title.bytes_after` should be `0` but i can loop till it comes out to be 0
var rez_title = ostypes.API('xcb_get_property_reply')(ostypes.HELPER.cachedXCBConn(), req_title, null);
// console.log('rez_title:', rez_title);
var title_len = ostypes.API('xcb_get_property_value_length')(rez_title); // length is not null terminated so "Console - chrome://nativeshot/content/resources/scripts/MainWorker.js?0.01966718940939427" will be length of `88`, this matches `rez_title.length` but the docs recommend to use this call to get the value, i dont know why
console.log('title_len:', title_len, 'rez_title.contents.length:', rez_title.contents.length); // i think `rez_title.contents.length` is the actual length DIVIDED by 4, and rez_title_len is not dividied by 4
var title_buf = ostypes.API('xcb_get_property_value')(rez_title); // "title_len: 89 rez_title.contents.length: 23" for test case of "Console - chrome://nativeshot/content/resources/scripts/MainWorker.js?0.01966718940939427"
// console.log('title_buf:', title_buf);
var title = ctypes.cast(title_buf, ctypes.char.array(title_len).ptr).contents.readString();
console.log('title:', title);
ostypes.API('free')(rez_title);
return title;
Sometimes though what is returned by xcb_get_input_focus_reply_t->focus is not the window to act on. I have found that sometimes it doesn't have a title, but if you use xcb_query_tree you can find its parent window probaby has a title:
var req_query = ostypes.API('xcb_query_tree')(ostypes.HELPER.cachedXCBConn(), win);
var rez_query = ostypes.API('xcb_query_tree_reply')(ostypes.HELPER.cachedXCBConn(), req_query, null);
console.log('rez_query.contents:', rez_query.contents);
if (root === -1) {
root = rez_query.contents.root;
}
win = rez_query.contents.parent; // this win should have the title