[C] Список PID из WM

#include <stdio.h>
#include <stdlib.h>

#include <X11/Xatom.h>
#include <X11/Xutil.h>

int main()
{
    Display *display = XOpenDisplay(NULL);

    if (display == NULL) {
        fprintf(stderr, "system error: XOpenDisplay");
        exit(EXIT_FAILURE);
    }

    Window window = XDefaultRootWindow(display);

    Atom net_wm_pid = XInternAtom(display, "_NET_WM_PID", True);

    if (net_wm_pid == None) {
        fprintf(stderr, "system error: can't find the _NET_WM_PID property");
        XCloseDisplay(display);
        exit(EXIT_FAILURE);
    }

    void traverse(void)
    {
        unsigned n, i;
        Window root, parent, *childs;

        Atom type;
        int format;
        unsigned long n_items, n_bytes;
        unsigned char *prop = NULL;

        if (Success == XGetWindowProperty
            (display, window, net_wm_pid, 0, 1, False, XA_CARDINAL, &type,
             &format, &n_items, &n_bytes, &prop)) {
            if (prop != NULL) {
                pid_t pid = *(pid_t*)prop;
                printf("%i\n", pid);
                XFree(prop);
            }
        }

        if (0 != XQueryTree(display, window, &root, &parent, &childs, &n)) {
            for (i = 0; i < n; i++) {
                window = childs[i];
                traverse();
            }
            XFree(childs);
        }
    }

    traverse();

    XCloseDisplay(display);
    exit(EXIT_SUCCESS);
}

/*
 * KLUDGE:
 *
 * ==30192== HEAP SUMMARY:
 * ==30192==     in use at exit: 124 bytes in 1 blocks
 * ==30192==   total heap usage: 1,655 allocs, 1,654 frees, 71,374 bytes allocated
 * ==30192== 
 * ==30192== 124 bytes in 1 blocks are definitely lost in loss record 1 of 1
 * ==30192==    at 0x4026864: malloc (vg_replace_malloc.c:236)
 * ==30192==    by 0x42D0902: ??? (in /usr/lib/i386-linux-gnu/libxcb.so.1.1.0)
 * ==30192==    by 0x42D0A04: ??? (in /usr/lib/i386-linux-gnu/libxcb.so.1.1.0)
 * ==30192==    by 0x42D03D1: xcb_connect_to_display_with_auth_info (in /usr/lib/i386-linux-gnu/libxcb.so.1.1.0)
 * ==30192==    by 0x42D05DB: xcb_connect (in /usr/lib/i386-linux-gnu/libxcb.so.1.1.0)
 * ==30192==    by 0x407FA22: _XConnectXCB (in /usr/lib/i386-linux-gnu/libX11.so.6.3.0)
 * ==30192==    by 0x406F8F3: XOpenDisplay (in /usr/lib/i386-linux-gnu/libX11.so.6.3.0)
 * ==30192==    by 0x80487B6: main (in /tmp/pids)
 * ==30192== 
 * ==30192== LEAK SUMMARY:
 * ==30192==    definitely lost: 124 bytes in 1 blocks
 * ==30192==    indirectly lost: 0 bytes in 0 blocks
 * ==30192==      possibly lost: 0 bytes in 0 blocks
 * ==30192==    still reachable: 0 bytes in 0 blocks
 * ==30192==         suppressed: 0 bytes in 0 blocks
 */

$ gcc -lX11 pids.c -o pids
pids.c: In function ‘main’:
pids.c:27:5: warning: ISO C forbids nested functions
$ ./pids
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32547
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4478
32547
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30756
2015
2015
13614
13614
2015
32547
32547
4847
4847
2015
4847