Frequently Asked Questions

  1. Will Qt continue to be free?

    A: We will continue to release free versions for the X Window System, and they will be free for free software development.

  2. The Qt demos I've seen only have one window. Can I have several windows in one application?

    A: Yes, easily.

  3. What kind of licenses exist for Qt?

    A: The Qt toolkit is available under several licenses; the free license for X, a license for shareware developers for X and a fully-fledged professional license.

  4. What are the differences between the professional and free versions of Qt?

    A: You can write commercial software using the professional license. The library itself is the same. You also get one year of free support when you buy a professional license.

  5. Can I write software for internal use in my company/organization using the free license?

    A: That depends. If you want to use the free license within an organization, your software must be intended for the free software community. Your software must be usable outside your organization (if anyone should want to use it) you must notify Troll Tech before starting to use it, you have to allow free distribution and you have to make your source code available.

  6. Can I write software under the GNU General Public License, GNU General Library Public License or BSD licenses using the Qt free license?

    A: Yes.

  7. Really? Your additional requirements seem to conflict with the GPL.

    A: Really yes. We require cooperation from you, in return you can use Qt. We could have demanded money (actually, we do for the professional licence) and still not have been in conflict with the GPL.

  8. I want to use Qt to develop free software on Windows.

    A: Qt is not free for Windows. We do however sell professional licenses.

  9. When will 1.0 be released?

    A: This question seems not to be a FAQ any more, so we've removed the answer.

  10. I don't want to give away my source. What do I do?

    A: Then you need a shareware or professional license.

  11. Can I charge for my application?

    A: If you have a professional license; of course. If you have a free license your software must be freely distributable and you must include the source.

    The free license is intended for free software. We realize that CD-ROMs cost money to produce, for example, so you can charge a copying fee.

  12. Where can I find Qt?

    A: The latest version of Qt can be downloaded from http://www.troll.no or from ftp.troll.no, or (less often updated) from sunsite.unc.edu in /pub/Linux/X11/devel/ (or /pub/Linux/Incoming).

    We encourage all developers of software that use Qt to upload their work to ftp.troll.no.

  13. Who is Troll Tech and what are your future plans?

    A: Troll Tech consists (now) of four talented, hard-working programmers who work day and night to improve Qt, and enjoy it. We started the company in 1994, but parts of Qt were written for earlier projects. The first line of code was written in 1992.

    Our income comes from selling Qt licenses and from a development contract with a customer; we develop code based on Qt for the Norwegian division of NCR (previously AT&T).

  14. Can I use Qt's classes without writing a graphical user interface?

    A: Quite a few of the classes can be used independently of the user interface. See utility classes, There are also a few classes that will work without the GUI only by chance.

  15. I want to port Qt to a new platform. What do I do?

    A: If the new platform is POSIX-like and runs the X Window System, it's simple. Read the file PORTING for details. If you succeed you can send us the patches. When we've added your patches to our source tree, Qt will officially support the new platform.

  16. Will Qt be available for [OS/2, Mac, Amiga]?

    A: At present, Qt only works well on X11 and Win32 (Windows 95 and Windows NT). Porting to other platforms is a lower priority. Currently, we concentrate on the Windows and X versions.

  17. Can I make a Qt shared library and distribute it with my Linux distribution?

    A: Yes, if you do not make changes to Qt and include all the files present in our distribution of Qt. (That is, you must include the source code.)

  18. Can I distribute dynamically linked applications that use Qt? Can I distribute statically linked applications that use Qt?

    A: Yes and yes, as long as you do not modify Qt.

  19. I need to modify Qt.

    A: Are you sure? Inheritance is very often a better alternative. If you do change Qt, you may not distribute the modified toolkit or programs using it.

    We encourage you to send patches to qt-bugs@troll.no. We will try to evaluate the patches and reply as soon as they come in. If we like what we see, we'll incorporate it in the next Qt release.

  20. Why can't I distribute modified versions of Qt? I want to distribute my application quickly, not wait for you to make a new Qt release.

    A: Having several different shared libraries with the same name is not a good idea. Having five libraries, equal except for minor bugfixes, in memory isn't a good idea either. Finally, we don't want support questions about libraries we have no knowledge of.

  21. How can I distribute my cool widget library?

    A: In several ways. Pick and choose.

    If the library is small, a widget or two, perhaps the best way is to submit it as a contribution to Qt.

    If it's larger, you can distribute it, and you can include Qt along with it. But you cannot include Qt as part of your library (e.g. by making a shared library which includes Qt and your library).

    People must still be aware that they are using Qt, and they must have a license for Qt.

    This applies to wrapper libraries as well, of course. If you write Ada or Perl bindings, fine. But anyone who uses your bindings must also have a license for Qt.

  22. I found this obscure bug and I need it fixed, fast!

    A: We sell support and maintenance contracts. We try to support the free users, and we take all bug reports seriously, no matter who they come from.

    But, of course, if there's too much to do we have to put more emphasis on paying customers.

  23. Is there a mailing list or something for Qt?

    A: There are two: qt-interest@troll.no and qt-announce.

    Qt-interest is a user forum. There can be as much as 20 messages per week. To join it, send a message containing the single word "subscribe" to qt-interest-request@troll.no.

    Qt-announce is for announcements of new Qt versions and a few other announcements. We expect that there will be less than ten messages to the list each year. To join the list, send mail containing the single word "subscribe" to qt-announce-request@troll.no.

    All messages to Qt-announce are also sent to Qt-interest, so you don't need to be on both lists.

  24. Do you have any plans for a graphical designer/dialog builder?

    A: We are working on one now. There will be further announcements on qt-interest and, as appropriate, qt-announce.

    There is also a free dialog editor written by Jeff Harris and Klaus Ebner. See http://www.cis.ohio-state.edu/~jharris/dlgedit/ for more information.


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