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Old 09-20-2004, 05:18 AM   #1
Registered: May 2001
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Developing software for KDE???


I have a general question regarding software developing for KDE.
I read at their homepage that KDE uses the QT-library.

I'm wondering if I have to use the QT-library too, to be able to create an application for the KDE desktop?

Cause this QT-library version is under GPL does this automatically make my application open source or is it possible to make a commersial application even if I use this QT-library?

Hope you understand my questions.

Old 09-20-2004, 05:28 AM   #2
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KDE applications actually use the KDE libraries, which are built on top of KDE. If you want to use these, then you will have to release your code under the GPL.

You can, however, write a pure Qt application that is commercial (rather than GPL) if you wish. You will have to buy a deveopers licence from TrollTech (

As an aside, the GPL doesn't stop you from charging money for software. Instead, it forces you to (among other things) release the source-code and allow anyone else who gets your software to modify your code and/or redistribute it as they please. It's designed to allow you to develop the best possible software by (primarily) allowing people who find bugs or limitations to fix them, and share their fixes.
Old 09-20-2004, 05:32 AM   #3
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But how can I charge money if I realease the source?

Then they just need to download the source and modify a line and no need to pay for it???
Old 09-20-2004, 05:46 AM   #4
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Read the GPL.

You'll see you have iirc three options if you sell someone something based on GPLed work: Send the source but charge only for the cost of the medium; send an offer valid for 3 years that you'll send the source on request; or the third one which iirc is for non-commercial and re-redistribution.

Then they just need to download the source and modify a line and no need to pay for it???
That's the point... You give up control of the future of your code, so that others may improve it where you do not. You dont have to give out the code to everyone, just those who buy a compiled version of your product iirc. But as stated you'll need a developement liciense from TrollTech for Qt and then you can be closed source.

Last edited by Proud; 09-20-2004 at 05:49 AM.
Old 09-20-2004, 05:50 AM   #5
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Isn't a better product more valuable than an unfixable one? You only need to release the source code along with the binaries. Plus you can make money from consultancy for the software (which is where the big money is anyway), paper documentation etc.

The programming forum isn't the right place for this debate. For more, see

To answer the original question again, you can write Qt (non-KDE) software without a releasing the source code if you buy a commercial development licence. See the TrollTech website.

Btw, TrollTech make money from Qt, and they release the source. One example of many.


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