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Two separate things: 1) The Qt source code. Available under GPL, LGPL or commercial license 2) Some extra proprietary addons. Only available under the commerc

Two separate things: 1) The Qt source code. Available under GPL, LGPL or commercial license 2) Some extra proprietary addons. Only available under the commercial license.

jordigh 12y ago
I don't get it, why would anyone buy an LGPL exception? They want to keep their own private Qt fork and keep the modifications to Qt locked up? Is the cost of maintaining a private fork really that profitable and much lower than the cost of buying an LGPL exception? I'm just surprised that's a good business model too. I don't quite understand it. Maybe there's something I could read instead of asking the lazyweb?
- zanny 12y ago
  You don't need to read much, the answer is simple: legal departments. For most companies, the lawyers don't understand the LGPL or software at all, so they don't understand that the LGPL lets the company distribute binaries with Qt libraries included without any source release requirements. They just need to include a notice that Qt is used and where to get the LGPL parts source. They just like being able to pay money and "own" the IP. The only time a company actually needs the commercial option is when they distribute in house modified Qt libraries, because those would be derivative works. And I would really want to know why the hell any company thinks its worth it to buy a commercial license so they don't have to release their modifications to Qt itself. That is just ridiculous.
  - FigBug 12y ago
    LGPL isn't compatible with app stores since the user can't relink. So you need a commercial license. As well, the licensing cost of the enterprise license is $200 a month, that's so cheap compared to a developers salary there isn't a lot of reason not to get it. Then you can do a static link and make your application a lot smaller (depending on what parts of Qt you actually use) and make installation simpler. I really like Qt, but I don't use it for a lot of my simple commandline apps because it would turn what could be a <500KB single .exe into a .exe that requires a few MB of DLLs.
- pavlov 12y ago
  LGPL allows only dynamic linking, i.e. the Qt libraries must remain separately loaded binaries and cannot be included into another project in object form. I could see some reasons why a company would want to statically link Qt libraries into a larger binary. For that they'll need the commercial license.
  - __david__ 12y ago
    That's not precisely correct. You can statically link proprietary code with LGPL code and even distribute it, but you must also distribute the object code such that the user can re-link against newer/changed versions of the library to create a new static binary.

Two separate things: 1) The Qt source code. Available under GPL, LGPL or commercial license 2) Some extra proprietary addons. Only available under the commercial license.

jordigh 12y ago

I don't get it, why would anyone buy an LGPL exception? They want to keep their own private Qt fork and keep the modifications to Qt locked up? Is the cost of maintaining a private fork really that profitable and much lower than the cost of buying an LGPL exception? I'm just surprised that's a good business model too. I don't quite understand it. Maybe there's something I could read instead of asking the lazyweb?

zanny 12y ago
You don't need to read much, the answer is simple: legal departments. For most companies, the lawyers don't understand the LGPL or software at all, so they don't understand that the LGPL lets the company distribute binaries with Qt libraries included without any source release requirements. They just need to include a notice that Qt is used and where to get the LGPL parts source. They just like being able to pay money and "own" the IP. The only time a company actually needs the commercial option is when they distribute in house modified Qt libraries, because those would be derivative works. And I would really want to know why the hell any company thinks its worth it to buy a commercial license so they don't have to release their modifications to Qt itself. That is just ridiculous.
- FigBug 12y ago
  LGPL isn't compatible with app stores since the user can't relink. So you need a commercial license. As well, the licensing cost of the enterprise license is $200 a month, that's so cheap compared to a developers salary there isn't a lot of reason not to get it. Then you can do a static link and make your application a lot smaller (depending on what parts of Qt you actually use) and make installation simpler. I really like Qt, but I don't use it for a lot of my simple commandline apps because it would turn what could be a <500KB single .exe into a .exe that requires a few MB of DLLs.
pavlov 12y ago
LGPL allows only dynamic linking, i.e. the Qt libraries must remain separately loaded binaries and cannot be included into another project in object form. I could see some reasons why a company would want to statically link Qt libraries into a larger binary. For that they'll need the commercial license.
- __david__ 12y ago
  That's not precisely correct. You can statically link proprietary code with LGPL code and even distribute it, but you must also distribute the object code such that the user can re-link against newer/changed versions of the library to create a new static binary.