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Comment by rgovostes | Hacker News Reader

To this newcomer to Qt, distributing standalone apps seems like a disaster. Binaries built for macOS link against Qt libraries in /usr/local; on Windows, you need to copy a dozen .dll files until your executable launches, or otherwise rebuild all of Qt (!) to support static linking.

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QT is distributed under LGPl so by statically linking you must also distribute your program as LGPL. My understanding is that allowing a user to link their own version of QT (ie shared/dynamic libraries are acceptable) fulfils the criteria to avoid licensing your project under LGPL.

>on Windows, you need to copy a dozen .dll files until your executable launches

Presumably you're new to Windows development? as long as you place the libraries in the same folder as the executable, add the QT install directory to your path, or add the install direvtoey to your debigging Environment variable, you're laughing - it's as straightforward as DLLs on Windows come.

> QT is distributed under LGPl so by statically linking you must also distribute your program as LGPL

AFAIK, static linking doesn't necessary make the whole project LGPL. You just need to provide users relink LGPL part of the library.

Would that mean that distributing object files and letting the user link their own QT would work? I'm not totally sure on the nuanced here unforrunately

Yes

Exactly. For example if you make a project with Qt5.11 then the user should be able to rebuild the project with Qt5.12.

yes, according to the GPL authors : https://www.gnu.org/licenses/gpl-faq.en.html#LGPLStaticVsDyn...

Cool, thanks! I've learned something today!

And bear in mind that 'object file' here could consist of simply a single 'ar' format file containing all the other static code that needs one simple link command.

> as long as you place the libraries in the same folder as the executable

The problem is that I don't know which libraries I need. For a very small project I just kept launching the .exe and reading error messages until I had gathered all the DLLs. It's not a sound way to do it, in case a library is loaded dynamically.

For Qt dlls, use windeployqt. For third-party libs you will still need to copy manually though

> For Qt dlls, use windeployqt.

This, and there are also applications which state which DLLs are missing from a deployment.

How would you have figured out which libraries you need if you were linking it statically? I'm not going to apologise for Windows DLL behaviour (side note, you can use `dumpbin /dependents` or `DependencyWalker` to track them down) as it's awful, but this is categorically nothing to do with QT.

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