How to get an X11 Window from a Process ID?

http://stackoverflow.com/questions/151407/how-to-get-an-x11-window-from-a-process-id

Under Linux, my C++ application is using fork() and execv() to launch multiple instances of OpenOffice so as to view some powerpoint slide shows. This part works.

Next I want to be able to move the OpenOffice windows to specific locations on the display. I can do that with the XMoveResizeWindow() function but I need to find the Window for each instance.

I have the process ID of each instance, how can I find the X11 Window from that ?

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UPDATE - Thanks to Andy's suggestion, I have pulled this off. I'm posting the code here to share it with the Stack Overflow community.

Unfortunately Open Office does not seem to set the _NET_WM_PID property so this doesn't ultimately solve my problem but it does answer the question.

// Attempt to identify a window by name or attribute.// by Adam Pierce <[e-mail]>#include <X11/Xlib.h>#include <X11/Xatom.h>#include <iostream>#include <list>using namespace std;class WindowsMatchingPid{public:    WindowsMatchingPid(Display *display, Window wRoot, unsigned long pid)    : _display(display)    , _pid(pid)    {    // Get the PID property atom.    _atomPID = XInternAtom(display, "_NET_WM_PID", True);    if(_atomPID == None)    {    cout << "No such atom" << endl;    return;    }    search(wRoot);    }    const list<Window> &result() const { return _result; }private:    unsigned long  _pid;    Atom           _atomPID;    Display       *_display;    list<Window>   _result;    void search(Window w)    {    // Get the PID for the current Window.    Atom           type;    int            format;    unsigned long  nItems;    unsigned long  bytesAfter;    unsigned char *propPID = 0;    if(Success == XGetWindowProperty(_display, w, _atomPID, 0, 1, False, XA_CARDINAL,                                     &type, &format, &nItems, &bytesAfter, &propPID))    {    if(propPID != 0)    {    // If the PID matches, add this window to the result set.    if(_pid == *((unsigned long *)propPID))    _result.push_back(w);    XFree(propPID);    }    }    // Recurse into child windows.    Window    wRoot;    Window    wParent;    Window   *wChild;    unsigned  nChildren;    if(0 != XQueryTree(_display, w, &wRoot, &wParent, &wChild, &nChildren))    {    for(unsigned i = 0; i < nChildren; i++)    search(wChild[i]);    }    }};int main(int argc, char **argv){    if(argc < 2)    return 1;    int pid = atoi(argv[1]);    cout << "Searching for windows associated with PID " << pid << endl;// Start with the root window.    Display *display = XOpenDisplay(0);    WindowsMatchingPid match(display, XDefaultRootWindow(display), pid);// Print the result.    const list<Window> &result = match.result();    for(list<Window>::const_iterator it = result.begin(); it != result.end(); it++)    cout << "Window #" << (unsigned long)(*it) << endl;    return 0;}

chingliu-desktop tmp # g++   -o getwindow getwindow.cpp   -I/usr/X11R6/include   -L/usr/X11R6/lib   -lX11