About Trolltech QT OpenSource license.

Kevin Walzer kw at codebykevin.com
Tue Apr 10 22:52:12 CEST 2007

king kikapu wrote:

> As i said, i do not fully understand all this license stuff. All i
> want to ask is, i can make GPL software and gain money from this ?

Yes. Nothing in the GPL prevents you from developing and marketing an 
application for as high a price as you can get from it.


you will have to distribute the source code to your application to 
anyone who purchases a binary from you.


they will be permitted under the GPL to redistribute your application, 
source code and all. The GPL would allow them to buy your application 
from you and then redistribute it at no cost to others.

Most commercial shrink-wrap software depends on enforcing restrictions 
on end users to compel a revenue stream: withholding some of the 
application's functionality prior to payment, hiding the locking 
algorithm inside obfuscated source code, and prohibiting modification 
and redistribution of the application and/or its code. If this is your 
business model, then the GPL is probably not for you.

If you use the GPL, you would have to make your locking alogrithim as 
plain as day; someone out there would likely have the knowledge to patch 
your software to work without the locking algorithm, assuming they 
obtained the binary and source code legally (either by purchasing it 
from you or obtaining it from someone who purchased it from you); and 
they would be legally free to redistribute the patched application, with 
or without cost.

Of course, there's no guarantee this will happen; such patching also 
happens with closed-source software. But many commercial developers look 
at the GPL and decide that this is a risk they do not want to take.


Kevin Walzer
Code by Kevin

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