x-window,XFetchName get null

[zjf_ha]

hi,I have a program with kde ,why windows' name is null with "XFetchName"
follow code:

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

static char *window_id_format = "0x%lx";
int main (void)
{
        unsigned int numkids, i, mapped, scrn;
        Window r, p, *kids;
        XWindowAttributes attr;
        Window root;
        Display *dipsy;
        char *win_name;
        dipsy = XOpenDisplay(0);
        scrn = DefaultScreen (dipsy);
        root = RootWindow (dipsy, scrn);

        mapped = 0;
        XQueryTree (dipsy, root, &r, &p, &kids, &numkids);

        for (i = 0; i < numkids; ++i)
        {
                XGetWindowAttributes (dipsy, kids[i], &attr);
                if (attr.map_state == IsViewable)
                {
                        ++mapped;
                        printf (window_id_format, kids[i]);

                        if (!XFetchName (dipsy, kids[i], &win_name))
                        {
                                printf ("(has no name %d \n)",mapped);
                                XFree (win_name);
                        }
                        else if (win_name)
                        {
                                printf (" %s \n", win_name);
                                XFree (win_name);
                        }
                }
        }
}

thanks very much~~

[zjf_ha]

I use XFetchName get window name ,I get null(has no name),but I can see title in the window,etc ,firefox named "xfetchname - Google serch - Mozilla Firefox",but i got null

why?

thanks very much

[Rubberman]

Please provide the code you are using.