MySQL plugin, mingw64 and Windows 8.1 - QMYSQL driver not loaded

Aggs · 10 May 2016, 07:32

I'm trying to make a Windows application that uses the Qt SQL plugin. With mingw32 this works fine, but when I try to build it as a 64bit application with mingw64 I get the following error:

QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers: QIBASE QSQLITE QMYSQL QMYSQL3 QODBC QODBC3 QPSQL QPSQL7
QSqlError("", "Driver not loaded", "Driver not loaded")

With the QT_DEBUG_PLUGINS flag set I get:

loaded library "C:/msys64/mingw64/share/qt5/plugins/sqldrivers/qsqlmysqld.dll"
QLibraryPrivate::loadPlugin failed on "C:/msys64/mingw64/share/qt5/plugins/sqldrivers/qsqlmysqld.dll" : "Cannot load library C:\\msys64\\mingw64\\share\\qt5\\plugins\\sqldrivers\\qsqlmysqld.dll: The specified module could not be found."
QSqlDatabase: QMYSQL driver not loaded

Trying to load qsqlmysqld.dll with LoadLibraryExA fails unless the DONT_RESOLVE_DLL_REFERENCES flag is used.

Looking at qsqlmysqld.dll in Dependency walker only flags the following two missing libs:
API-MS-WIN-CORE-SHUTDOWN-L1-1-1.DLL
EXT-MS-WIN-NTUSER-UICONTEXT-EXT-L1-1-0.DLL

However I have no idea what these libs do, where the come from or why they are missing.

So my questions are:

Are the above 'missing' dlls important?
If so, where are they?
If not, why dosn't the MySQL plugin work?
Any other thoughts/suggestions?

Also, libmysql.dll - this is located in the same folder as the executable, is a 64bit version and loads successfully with LoadLibraryExA so libmysql.dll doesn't seem to be the problem.

ARASHz4 · 10 May 2016, 07:16

you Should copy 'libmysql.dll' inside app folder

Aggs · wrote on 10 May 2016, 07:16

@ARASHz4 I did - see the last sentence of the OP.

SGaist · 10 May 2016, 07:46

Hi and welcome to devnet,

Did you build both debug and release version of Qt ?

The error message says that it can't find qsqlmysqld.dll which is the debug version of the plugin.

the_ · 5 Oct 2016, 07:33

@Aggs
/DELETED/ @SGaist was a bit faster with the same question :)

Aggs · S SGaist 10 May 2016, 07:32

@SGaist I didn't build Qt - I just downloaded the pre-compiled binary.

I have been building my application in debug mode - which I assume is why qsqlmysqld.dll is been used.

I just tried building a release version and it results in all the same errors but with qsqlmysql.dll instead.

SGaist · 10 May 2016, 09:26

Which version did you install exactly ?

Aggs · S SGaist 10 May 2016, 09:03

@SGaist The details from Qt Creator's option menu:


Name: Qt 5.6.0 (mingw64)
ABI: x86-windows-msys-pe-64bit
Source: C:\msys64\mingw64
mkspec: win32-g++
qmake: C:\msys64\mingw64\bin\qmake.exe
Default: debug
Version: 5.6.0
QMAKE_SPEC win32-g++
QMAKE_VERSION 3.0
QMAKE_XSPEC win32-g++
QT_HOST_BINS C:\msys64\mingw64\bin
QT_HOST_DATA C:\msys64\mingw64\share\qt5
QT_HOST_LIBS C:\msys64\mingw64\lib
QT_HOST_PREFIX C:\msys64\mingw64
QT_INSTALL_ARCHDATA C:\msys64\mingw64\share\qt5
QT_INSTALL_BINS C:\msys64\mingw64\bin
QT_INSTALL_CONFIGURATION 
QT_INSTALL_DATA C:\msys64\mingw64\share\qt5
QT_INSTALL_DEMOS C:\msys64\mingw64\share\qt5\examples
QT_INSTALL_DOCS C:\msys64\mingw64\share\qt5\doc
QT_INSTALL_EXAMPLES C:\msys64\mingw64\share\qt5\examples
QT_INSTALL_HEADERS C:\msys64\mingw64\include
QT_INSTALL_IMPORTS C:\msys64\mingw64\share\qt5\imports
QT_INSTALL_LIBEXECS C:\msys64\mingw64\share\qt5\bin
QT_INSTALL_LIBS C:\msys64\mingw64\lib
QT_INSTALL_PLUGINS C:\msys64\mingw64\share\qt5\plugins
QT_INSTALL_PREFIX C:\msys64\mingw64
QT_INSTALL_QML C:\msys64\mingw64\share\qt5\qml
QT_INSTALL_TESTS C:\msys64\mingw64\share\qt5\tests
QT_INSTALL_TRANSLATIONS C:\msys64\mingw64\share\qt5\translations
QT_SYSROOT 
QT_VERSION 5.6.0

SGaist · 10 May 2016, 10:05

I meant where did you get that package ?

Aggs · S SGaist 10 May 2016, 09:42

@SGaist Oh, I used MSYS2 to install it with the command: pacman -Sy mingw-w64-{i686,x86_64}-qt5

Qt Creator is the GPL Windows version from the main site. (this is 32bit which I thought might cause problems but everything else seems to work - I can compile and run 64bit applications that don't use MySQL)

SGaist · 11 May 2016, 00:03

For Qt Creator, no there's no influence. It only uses Qt, the architecture of it is of no importance for the functionality (unless of course you are building a plugin for it)

Silly question but: do you have a MinGW64 build of MySQL available on your machine ?

Aggs · S SGaist 10 May 2016, 19:57

@SGaist I don't have MySQL database installed on this machine (as I have another machine setup as a server with it)

I have a 64bit version of MySQL Workbench which was installed from the pre-compiled binaries. This contains the 64bit libmysql.dll which I am using.

Somehow I also have a 32bit version of libmysql.dll although I'm not quite sure where this came from. I've been using it for some time as it works when I compile a 32bit version of my application.

SGaist · 13 May 2016, 01:45

Then I wonder if the 32bit version of libmysql is found before the 64bit version.

Aggs · 13 May 2016, 01:59

@SGaist I don't think so. When I remove the 32bit libmysql.dll file the 32bit version of my app stops working but the 64bit version still doesn't work.

And when:
LoadLibraryExA("libmysql.dll", NULL, NULL);
is called, it successfully loads the library on both the 32bit and 64bit versions of my app.

Aggs · A Aggs 13 May 2016, 01:45

This is the dependences from qsqlmysql.dll (http://imgur.com/MUMHGfN)

Just noticed that it seems a bit odd that libmariadb.dll is needed but libmysql.dll isn't?

Aggs · wrote on 13 May 2016, 02:15

And that was the problem. I added libmariadb.dll to the same folder as the executable (same place as libmysql.dll) and now it all works!

Why I need a MariaDB library to connect to a MySQL database is still a mystery to me though... In fact libmysql.dll isn't even used - I just removed it and it still works.

Thanks for the help anyway! (if I can work out how, I'll mark this thread as solved)

SGaist · wrote on 13 May 2016, 06:15

MariaDB is a drop-in replacement for MySQL and AFAIK, you should be able to connect to MySQL servers through the MariaDB client libraries.