QSqlDatabase Driver not loaded

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Hello, I have a problem while connecting to a database via QtSql. This is a fragment of my code:

QCoreApplication a(argc, argv);
QSqlDatabase db = QSqlDatabase::addDatabase("SQLFileDatabase");
db.setHostName(host);
db.setDatabaseName(nazwa);
db.setUserName(login);
db.setPassword(haslo);
bool ok = db.open();

This is the error I get: pastebin. I have tried moving .lib files and sqldrivers to the .exe directory but it does not help (as you can see in the log).
I am using 32-bit QtCreator and Visual Studio 2017. Thanks for help.

SGaist

Hi and welcome to devnet,

Unless you wrote your own driver, SQLFileDatabase doesn't exist. It's QSQLITE if you are thinking about using a SQLite database.

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I replaced SQLFileDatabase with QMYSQL and now I get this error:

Cannot load library C:\Qt\5.11.1\msvc2017_64\plugins\sqldrivers\qsqlmysqld.dll: Unknown error 0x000000c1.
QLibraryPrivate::loadPlugin failed on "C:/Qt/5.11.1/msvc2017_64/plugins/sqldrivers/qsqlmysqld.dll" : "Cannot load library C:\\Qt\\5.11.1\\msvc2017_64\\plugins\\sqldrivers\\qsqlmysqld.dll: Unknown error 0x000000c1."
QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QMYSQL QMYSQL3 QODBC QODBC3 QPSQL QPSQL7

It works only for QSQLITE.

SGaist

Did you install the needed dependencies ?

If you set the QT_DEBUG_PLUGINS environment variable to 1 in the Run part of the Project panel, you will see why the plugin is not loaded.

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This is the log with enabled variable: pastebin. The qsqlmysqld.dll file exists but it does not work (log from previous post). What are the dependencies?

hskoglund

Hi is there any difference if you put libmysqld.dll in the same directory as your .exe file?

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I already have it in the same directory. However, I don't know it if works. It seems that it isn't detected by the program:

QFactoryLoader::QFactoryLoader() looking at "C:/Qt/5.11.1/msvc2017_64/plugins/sqldrivers/libmysqld.dll"
"Failed to extract plugin meta data from 'C:/Qt/5.11.1/msvc2017_64/plugins/sqldrivers/libmysqld.dll'"
         not a plugin

SGaist

As @hskoglund wrote: in the same folder as your application executable, not in the folder of the plugin.

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It is in the .exe and also plugin folder. I deleted the one from plugin directory and now log looks like this: pastebin - the libmysqld.dll file is not even loaded. This is the plugin folder: imgur and the .exe directory: imgur

hskoglund

Hmm that error 0x000000c1 could mean your 64-bit MySql is not installed 100%.

If you compile in Release mode instead of Debug, you get that same error 0x000000c1?

Edit: also check that you indeed installed the 64-bit version of MySql and not the 32-bit version, easiest way to check:
mysql.exe --V

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I had 64-bit MySql Server and 32-bit C Connector so I replaced it with 64-bit C++ Conector. I have tried compiling in the Release mode with no success. Should I reinstall the Qt libraries?

Cannot load library C:\Qt\5.11.1\msvc2017_64\plugins\sqldrivers\qsqlmysql.dll

I think this may be the problem - file is in the directory but is not recognized by the program.

hskoglund

I think the qsqlmysql.dll file is ok, but since it's depending on libmysql.dll being present in the same directory as your Qt .exe file, if that libmysql.dll is 32-bit, then you could have an error anyway.

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Can I download it (64 bit, Qt 5.11.1) without reinstalling the whole Qt?

hskoglund

I think you can do it by downloading the offline installer (never tried it) but easiest is most likely just to start MaintenanceTool.exe, remove the 5.11.1 MSVC2017 64-bit component and then selecting/installing it again.

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I have reinstalled the Qt libraries and replaced all the files in the exe directory with the newer version, and it works now. This is what I have in the folder: exe file, libmysql.dll, Qt5Core.dll and Qt5Sql.dll (in release mode).

Thank you for help!