I know it is weird but I need to execute a Qt GUI application that supports X11 protocol on MS Windows platform.
It is obvious that if I build my Qt source code in Unix environment it automatically becomes an X11 application and this application can be run only on Unix Operating Systems, not MS Windows.
I tried to use MXE (MinGW cross environment) to compile my application in Unix for Windows, but it does not help for X11 issue. It creates an application for Windows but the application is not an XWindow application.
There is also a XPortMinGW project for minGW. But I do not know if it works for Qt applications.
Is there any way to build my Qt application with X11 support that can run in Windows OS?
I don't think that there's any need for cross-compilation. There are two problems:
Getting Xlib compiled for Windows. I don't know offhand of any maintained Xlib implementations that are ported to Windows. You will definitely need to find one, or make one. Hopefully Xlib depends only on a handful of posix APIs and they may be easy to translate to win32. Forget about Cygwin.
You may have luck porting Xlib yourself to Qt's network backend and making it cross-platform in the process, too. Xlib would simply use the core and network modules of Qt. No problem with that.
The good news here are that Qt 5 comes with a bundled Xlib implementation. It would be presumably much easier to get that to compile on Windows than some other implementation.
Configuring Qt to build using said Xlib on Windows. To do it right, you'll probably want to mess a bit with and rebuild the configure tool that comes with Qt, and add a makespec that will link with the Xlib.
This should be much easier to do with Qt 5.
It's not an entirely trivial thing to do, but should be possible. Give yourself a month and expect to get very intimate with some details of Qt's configuration and Xlib.
Notes About Cygwin
If your application is closed-source and distributed outside of your organization, you need to buy a commercial license in order to redistribute cygwin.dll. Otherwise, Cygwin is GPL and merely linking to cygwin.dll makes your application a derived work.
Cygwin becomes problematic when you mix posix- and non-posix code in the same application, especially if the non-posix code is a large framework like Qt. You can of course use the Posix platform code in Qt and make it all run on Cygwin, but that way you lose performance and expose yourself to shortcoming of Cygwin's emulation of POSIX APIs.
Using Cygwin for Xlib / windowing system but having Qt otherwise use Windows APIs may require a lot of tweaking for Qt code. So may using Qt with Xlib on Windows of course, but at least you don't have to debug/work around Cygwin's quirks.
I have to port the application which is using the Qt3 library to a new embedded OS.
If the OS is not yet selected but it is known that it is not Linux/Windows, what is the general way of porting procedure? I mean what files should be changed and what are independed and can be left as is?
If it's not Linux or Windows you could be pretty stuck out the door. Qt is highly dependent on libraries being available for it to be able to build. This is not a no however, it has been ported to Symbian which is obviously not Linux or Windows. The big thing on that though is that it was ported by Nokia, who had amount of time and amount of developers, where those X's are reasonably big numbers.
Start by getting the Qt everywhere source code, work out what bits you're going to need and which bits you won't. If the platform has gcc/g++/another reasonably well understood C++ compiler you're in luck and you should be able to build the bits as needed. Qt does depend on standard libraries throughout so make sure they're also available in some form for the platform, and it does use some non-standard ones for some components so you'll need to know which aspects of Qt you're working on. You should be able to get some sort of toolchain from there.
I'd stick to platforms that Qt supports though, if you go off the beaten track you're looking into increasing your dev times and having very little useful support.
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Can someone suggest what's the best uses for those libraries today? Is it just GUI, or do they have database, XML, networking, threading, etc support too?
I was reading about them, and considered starting to learning/using one of them.
What is the most common one? What's the difference between them? Why would you choose one over the other?
As you seem to primarily target Linux, then the choice mostly depends on the programming language you want to use.
If you code in C, then obviously go for GTK+
If you code in C++, go for Qt, otherwise you will need Gtkmm (a C++ wrapper over GTK+)
If you code in Python, both GTK+ and Qt have bindings for the language: see PyGtk, PyQt and PySide (the one launched by Nokia themselves).
If you code in Java, Qt is no more a viable option imho as Nokia discontinued Qt Jambi (the Java bindings for Qt).
Also, Qt is more top-notch regarding its scenegraph QGraphicsScene API, its scripting engine built over Javascript Core (the engine powering WebKit), its state machine and animations framework, and the declarative UI.
GTK+ doesn't offer that much although you can use Clutter alongside with it.
If you're specifically looking into DB, XML (GTK+ has a parser for a subset of XML) and threading (GTK+ has GLib) features then Qt will offer all that in QtSql, QtXml and QtConcurrent.
All in all, I would say Qt is a sure choice. But GTK+ is very capable as well.
I'm not sure you will get a crystal clear answer for your question, which explains why some people keep preferring Gnome over KDE or vice-versa. Choose what works best for you.
PS: I you plan to also target Symbian, then go for Qt.
EDIT: Something that is also great with Qt is QtWebView: it brings Chromium into your Qt application to display web content. Others are embedding web content into their application using for instance Awesomium or Berkelium.
I've used GTK+, QT and wxWidgets before. Here's a brief summary:
For my first cross platform UI project I decided to go for wxWidgets mainly because at the time the license wasn't as restrictive as QT's (QT was GPL and only for Linux) and it had platform specific UI (unlike GTK). The project worked out well but there were quite a few glitches getting it to compile and run properly in other platforms - sometimes some events were fired up differently and such. Also GDI in wxWidgets was pretty slow.
Next I used GTK for a different project in python. For this I used the python bindings and everything worked out more or less smoothly. I didn't quite like the fact that the UI didn't look native on Windows and Mac and also when you launch a GTK+ app it always debug outputs loads of CRITICAL warnings which seem fine to ignore. :S
Finally, I did a very simple QT project now that Nokia has acquired it and was brilliant. The best of the three. First off, if you're not an old schooler who prefers VI or Emacs, QtCreator is brilliant. I really love VI and used it for years but I much prefer QtCreator for C++ QT projects. Regarding the library I also liked a lot the documentation and the APIs provided. QT has a concept of slots and signals which introduce new C++ keywords and a preprocessor. Basically, after reading a tutorial you'll get it easily and will start to love it. I'm now doing iPhone dev and it does feel a bit like Cocoa's/Interface Builder's UI paradigm.
Summary: I'd go for QT hands down. The license is pretty good and the SDK and documentation really nice.
I have never used GTK, but from my personal experience using Qt:
It is much more than a simple GUI. It's a whole application framework. I used to think of it as the Java libraries for C++. It provides all you mention -- database, XML, networking and threading, and more. It also provides things such as containers and iterators, and counterparts to a number of boost libraries.
The thing that impressed me most when starting to use Qt was the extremely extensive documentation. You get a program called Qt Assistant, which provides fully indexed and searchable API documentation on your desktop, as well as numerous code examples and tutorials. I found it made a big difference in searching the web each time for API info. Very quick access when you need to remember a method signature.
I am not sure which is most common; that's probably hard to measure accurately. They're certainly both popular. As Gnome is the default desktop of Ubuntu, and Gnome sits on top of GTK, it obviously has widespread usage. Of course, KDE is very popular as well. Nokia is heavily pushing Qt in the mobile space -- their Maemo OS, used on the new N900 for example, is soon to switch to Qt as the default toolkit (currently it is GTK.) I believe Qt will also soon become the default toolkit for Symbian OS.
I have not used Qt Creator, but I have heard many good things about it. It is a C++ IDE with obvious heavy integration with Qt. It also has fake vim emulation which is always nice if you like that kind of thing!
Qt uses qmake for build configuration. I found this much nicer than having to write your own makefiles. I do not know what GTK uses for building.
A couple of things I found a bit offputting with Qt at first was its big uses of preprocessor macros. The signal/slots system provides a nice mechanism for event/message passing in your application, but it does feel a bit like magic that may not be easily portable to another toolkit if you ever want to. Also, the moc (meta-object compiler), while I'm not entirely sure what it does, also feels a bit too much like magic going on behind the scenes.
All in all, though, I would recommend Qt, particularly if you are learning. It has really amazing documentation and a nice IDE, and busy forums. You'll be able to build C++ apps very rapidly with it, particularly with the QML coming in 4.7.
It probably depends on what you want to do. I would recommend Qt, because it's more than GUI, it has nice Python bindings (so does Gtk), and GUI libraries themselves are (subjectively speaking) more pleasant then Gtk.
Gtk is on the other hand more common in linux world, so you can probably get more help on the web. Reason for widespread of Gtk probably has more to do with Gnome and Ubuntu, rather then technical merits, but if you want you software to blend nicely with those two, you'll achieve that more easily with Gtk.
Qt for one sure has solid DB, network, threading support etc... It does a lot more then just cross-platform GUI (and it does most of it quite well).
I'd recommend it over GTK+.
Qt. It's not only object oriented, is "good" object oriented.
It's based on a "subset" of C++ that doesn't rely on the obscurity of C++ (but you are allowed to stick with them, if you fancy masochism ;) ).
It has a strong momentum now that Nokia bought it (actually Nokia did ~2/3 years ago). It's going to be in all Nokia AND Intel mobile devices (smartphones, netbooks, tablets).
It's the backbone of KDE, so it's very mature, but it's designed in a very flexible way, that makes it possible to support TODAY all the latest "cool stuff" that a more-then-just-GUI framework should have.
Go for it.
Just adding QT advantages to other answers.. QT has great documentation, its own IDE & GUI creator and enhances C++ with some new concepts like slots/signals (basically events).
I am not a GTK developer, so I can't compare those to the GTK world :(
It also looks like Nokia is about to use Qt everywhere, like on Maemo
If you want your app to run on iOS, Android, Blackberry, other mobile platforms, Windows, Mac OSX, and Linux, use Qt.
qt-project.org
I have started using Python for web development recently, it's kinda cool;
I have seen programs that are developed in QT/C++, which is good enough in terms of esthetics;
I have just noticed the new PySide project (which brings LGPL Qt license to Python and it doesn't support Windows yet).
In view of the above, I see the possibility of using Python + PyQt/PySide to develop cross platform apps in the future :) but I have several doubts right now:
Can PyQty/PySide be used to develop really complex/modern UI? Can somebody give me some points to have a look at some nice-looking screenshots of apps that are developed in Python+QT?
What about the performance of using Python + QT for a desktop app?
Thanks in advance!
Can PyQty/PySide be used to develop really complex/modern UI?
Desktop applications come in all sorts of varieties -- some nicely laid out, some extremely customized with virtually no semblance to a standard application for that OS. The same can be done with Qt/PyQt/PySide. As Alex said, there should be no visible difference between an application written with PyQt/PySide versus one written with Qt in C++. Any program written with Qt4 (using bindings or not) will, by default, look like a standard modern application.
Of course, there are features of recent Windows releases (and likely some on Mac OS X) that aren't supported immediately and by default in Qt, but you can almost always write some custom platform specific code for those situations where said features are truly important.
Can somebody give me some points to have a look at some nice-looking screenshots of apps that are developed in Python+QT?
The best and most open source program that I know of and which is written with PyQt, is Eric -- a Python based IDE.
What about the performance of using Python + QT for a desktop app?
For most applications the performance difference between a C++ Qt application and a PyQt application are not noticible. But if you really need performance, you can write certain parts of the application in C++ and make bindings available in Python so you can integrate the two.
TortoiseHg was re-designed using Qt and PyQt for its 2.0 release.
Here is one of several posted screenshots:
There is no aesthetic difference between the look and feel of C++ based Qt, and the PyQt and PySide wrappers on top of it. I use basically no desktop GUI apps so I couldn't point you to any implemented with any of these language/toolkit combos, but if you like the former, you'll be hard put to distinguish it in any way from the latter.
A bit late but for the record, apps such as Skype, GoogleEarth or the recent versions of VLC (media player & more) used the Qt libs.
I will make a desktop application. I searched on web which one is better. Can someone say positive and negative sides of these components.
I can add some information about QT:
QT is a well designed, portable library that covers nearly everything you'll need for a desktop application. QT covers GUI, networking, SQL, Graphics and more.
Pros:
very extensive library
high performance
portable
Cons:
It's C++
special preprocessor / make tool needed.
Setting up a QT compile environment is a little bit more difficult than setting up a C++ compile environment. C++ is - especially if you are not used to it - very difficult and the learning curve is steep. QT helps alot with appropriate helper classes (QPointer, ...) and library magic (QObjects freeing children, ...) in the background. There are bindings to other languages as well. Just to mention a few - Jambi is a binding for Java and there's a binding for python as well.
For your decision consider the following things
which programming language do you know best
which libray reduces your amout of work for this application the most
how much performance do you REALLY need. C++ code can be very fast, but there's no reason to work with manual memory management and pointers if you don't need the performance.
which library offers you the look and feel you want to have for your desktop application
If you need portability: Do you want to "compile once run everywhere" (Java) or do you want to "run your app everywhere once you compiled it for this plattform" (QT)
Here's the link to QT-Jambi Wiki: http://qt.gitorious.org/qt-jambi/pages/Home. According to Nokia: "Qt Jambi is the Qt GUI toolkit for Java developers"
Qt is the best cross platform GUI framework at the moment. It renders the widgets with a native look on each platform and it has a very easy to use API.
Using Qt doesn't mean that you have to use C++. You can program Qt in Java (Qt Jambi) or Python (PyQt) for instance.