gistfile1.txt

// Attempt to identify a window by name or attribute.
// by Adam Pierce <adam@doctort.org>

#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <iostream>
#include <list>
#include <string>

class WindowsMatchingPid
{
public:
    WindowsMatchingPid(Display *display, Window wRoot, std::string name )
    	: _display(display)
    	, _name(name)
    {
    // Get the PID property atom.
    	_atomPID = XInternAtom(display, "_NET_WM_NAME", True);
    	if(_atomPID == None)
    	{
            std::cout << "No such atom" << std::endl;
    		return;
    	}

    	search(wRoot);
    }

    const std::list<Window> &result() const { return _result; }

private:
    Atom           _atomPID;
    Display       *_display;
    std::list<Window>   _result;
    std::string    _name;

    void search(Window w)
    {
    // Get the PID for the current Window.
    	Atom           type;
        Atom           utf8Atom = XInternAtom( _display, "UTF8_STRING", false );
    	int            format;
    	unsigned long  nItems;
    	unsigned long  bytesAfter;
    	unsigned char *retName = 0;
    	if(Success == XGetWindowProperty(_display, w, _atomPID, 0, 1, False, utf8Atom,
    	                                 &type, &format, &nItems, &bytesAfter, &retName))
    	{
    		if(retName && std::string((char*)retName) == _name )
    		{
                std::cout << "got temp name: " << retName << std::endl;
                std::cout << "window id = : " << w << std::endl;
    		// If the PID matches, add this window to the result set.
    			//if( 0 == strcmp( _name.c_str(), (char*)retName ) )
    		//		_result.push_back(w);

    			XFree(retName);
    		}
    	}

    // 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]);
    	}
    }
};



// USE IT LIKE THIS



#include "mainwindow.h"
#include "ui_mainwindow.h"

#include "windowId.h"

#include <QVBoxLayout>
#include <QTimer>
#include <QWindow>
#include <QProcess>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    auto pid( 18830 );

// Start with the root window.
    Display *display = XOpenDisplay(0);

// find the window whose name is "view", print its window ID
    WindowsMatchingPid match(display, XDefaultRootWindow(display), "view");

// Print the result, should only get one
    const std::list<Window> &result = match.result();

    for(std::list<Window>::const_iterator it = result.begin(); it != result.end(); it++)
    	std::cout << "Window #" << (unsigned long)(*it) << std::endl;