QEventLoop: Cannot be used without QApplication. Error in a multi-threaded library

I'm making a library which contains a QThread object. I am going with the moveToThread style.
The DLL is successfully loaded but Qt Creator's application output gives QEventLoop: Cannot be used without QApplication.
I've done some searching work and it suggests I need a QApplication. I don't have a main() in the library so I have no idea where I can put the QApplication object.
Thanks in advance.

The library itself should not instantiate QApplication, but every program loading it should.

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Originally Posted by yeye_olive

The library itself should not instantiate QApplication, but every program loading it should.

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Yes I think so. But it just gives this error. My loader is a normal Qt GUI which already has QApplication.
Oh what if the load is not a Qt program which does not have any QApplication?

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Originally Posted by hind

But it just gives this error. My loader is a normal Qt GUI which already has QApplication.

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You probably get this error because some QEventLoop is allocated by the library before the QApplication instance by the program. Does your library have a global variable (or static member field) of a QObject-derived type?

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Originally Posted by hind

Oh what if the load is not a Qt program which does not have any QApplication?

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Then you should not use QThread (and more generally QObjects) in your library as it depends on Qt's event loop for signal delivery.

Quote:

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Originally Posted by yeye_olive

You probably get this error because some QEventLoop is allocated by the library before the QApplication instance by the program. Does your library have a global variable (or static member field) of a QObject-derived type?


Then you should not use QThread (and more generally QObjects) in your library as it depends on Qt's event loop for signal delivery.

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Thank you for your replies. But when I accidentally swithed the loader from debug to release, the problem is gone...
And thanks for the second answer.