Unable to load qodbc driver not loaded

[durgeshK]

Hi All,

We are trying to create a DLL in C++(VS2005) using some of the Qt4.3.3 functionality(QtCore and QtSql). When i try to access this DLL from other C++ projects, its giving an error saying "Unable to load qodbc".

In Normal Qt application , we can use addLibrayPath to add the plugins related to database and image, but how can we do this in a DLL project.

Thanks & Regards,
durgesh

[giesbert]

This is a core problem when you use Qt in dlls and use those dlls from non qt binaries. Some Qt functions require a Q(Core)Application instance.

You could load a plug-in "by hand". It's a bit tricky...

@
QLibrary lib(QLatin1String("qtaccessiblewidgets4"));
if(lib.load())
{
QtPluginInstanceFunction pInstanceFct = 0;
QObject* pAccPlugin = 0;
pInstanceFct = (QtPluginInstanceFunction)lib.resolve("qt_plugin_instance");

        if(0 != pInstanceFct)
        {
            qRegisterStaticPluginInstanceFunction(pInstanceFct);
            bLoaded = true;
        }
    }

@

it should work with most plug-ins :-) They just have to be found by the path.

[durgeshK]

@Gerolf, Since i am using Qt4.3.3, i can't find some of the keywords like "qRegisterStaticPluginInstanceFunction" etc in my version.

i just used the following in the dll function

QLibrary lib(QLatin1String("C:\Qt\4.3.3\plugins\sqldrivers\qsqlodbcd4.dll"));
if(lib.load())
{
lib.resolve("qt_plugin_instance");
}
else
{
MessageBoxA(NULL,"Unable to load qodbc","Error",1);
exit(-5);
}

Now since i am not getting any MessageBox, i assume that i was able to load the plugin library. But again i am using this dll in another C++ console application, i am getting the error QODBC Driver not loaded.

[durgeshK]

Sorry for the above code the Code is as follow :

@QLibrary lib(QLatin1String("C:\Qt\4.3.3\plugins\sqldrivers\qsqlodbcd4.dll"));
if(lib.load())
{
lib.resolve("qt_plugin_instance");
}
else
{
MessageBoxA(NULL,"Unable to load qodbc","Error",1);
exit(-5);
}@

[giesbert]

You only loaded a library, but did not add the plug in.

@
typedef QObject *(*QtPluginInstanceFunction)();
@

can be found in qplugin.h. And without a call to qRegisterStaticPluginInstanceFunction the plugin is not registered in the global plugin cache. Without registration, it's not usable.