Plugin can load or not depending on whether my app is launched from Qt Creator or not

[agarny]

Hi, I am having an unexplained behaviour using Qt 4.7.3 and Qt Creator 2.2.1 on Windows 7 (everything works fine on Ubuntu 10.10 and Mac OS X 10.6 using the same versions of Qt and Qt Creator).

Basically, my application relies on various plugins being loaded upon starting my application. Now, for some weird reason, there is one out of 10 plugins that doesn't load when running my application from outside Qt Creator while if I start my application from within Qt Creator, then the plugin loads fine! This is the case whether I build a debug or release version of my application.

As I said, everything works fine on Linux and Mac OS X, so I am really puzzled as why that particular plugin doesn't load. Why that plugin?!

I know it might be a very long shot, but is there something trivial that I might have overlooked?

Here is some code that I use (before actually loading the plugin) to retrieve some information about the plugin itself:

PluginInfo Plugin::info(const QString &pPluginFileName)
{
    // Return the information associated to the plugin
 
    PluginInfo pluginInfo;
 
    typedef PluginInfo (*PluginInfoFunc)();
 
    PluginInfoFunc pluginInfoFunc = (PluginInfoFunc) QLibrary::resolve(pPluginFileName,
                                                                       QString(name(pPluginFileName)+"PluginInfo").toLatin1().constData());
 
    if (pluginInfoFunc)
        // The plugin information function was found, so we can extract the
        // information we are after
 
        pluginInfo = pluginInfoFunc();
    else
{
        // The plugin information funciton couldn't be found which means that
        // we are not dealing with an OpenCOR plugin
 
        pluginInfo.type = PluginInfo::Undefined;
 
if (!name(pPluginFileName).compare("CellMLModelRepository")) {
    QLibrary lib(pPluginFileName);
 
    if (lib.load())
        QMessageBox::information(0, QString("Info"), "Can load...");
    else
        QMessageBox::information(0, QString("Info"), QString("Can NOT load... [%1 | %2]").arg(pPluginFileName,
                                                                                              QFileInfo(pPluginFileName).exists()?"YES":"NO"));
}
}

PluginInfo Plugin::info(const QString &pPluginFileName)
{
    // Return the information associated to the plugin

    PluginInfo pluginInfo;

    typedef PluginInfo (*PluginInfoFunc)();

    PluginInfoFunc pluginInfoFunc = (PluginInfoFunc) QLibrary::resolve(pPluginFileName,
                                                                       QString(name(pPluginFileName)+"PluginInfo").toLatin1().constData());

    if (pluginInfoFunc)
        // The plugin information function was found, so we can extract the
        // information we are after

        pluginInfo = pluginInfoFunc();
    else
{
        // The plugin information funciton couldn't be found which means that
        // we are not dealing with an OpenCOR plugin

        pluginInfo.type = PluginInfo::Undefined;

if (!name(pPluginFileName).compare("CellMLModelRepository")) {
    QLibrary lib(pPluginFileName);

    if (lib.load())
        QMessageBox::information(0, QString("Info"), "Can load...");
    else
        QMessageBox::information(0, QString("Info"), QString("Can NOT load... [%1 | %2]").arg(pPluginFileName,
                                                                                              QFileInfo(pPluginFileName).exists()?"YES":"NO"));
}
}

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So, what happens is that I am trying to resolve a function which should be in my plugin. In all cases, it works but for that CellMLModelRepository plugin of mine. Having added some debug code, if the function cannot be found, I try to load the plugin using QLibrary which here fails for my CellMLModelRepository plugin even though QFile::exists() does report that the file exists...

[caduel]

Have you tried to output QLibary::errorString() ?
This helps alot in tracking down such things :-)

Maybe the plugin is not found at all, or some environment stuff (like QT_PLUGIN_PATH) is not set?

HTH

[agarny]

Yes, indeed... However, QLibrary::errorString() only tells me that "the specified module could not be found". Yet, QFile::exists() tells me that my plugin does exist... and as mentioned in my original message, it works fine from within Qt Creator. As for QT_PLUGIN_PATH, I will have a look (didn't know about that one), but still I can't understand why my other plugins would load fine since they are in the exact same directory...

[ChrisW67]

Your library is failing to load because either:

1. The library file itself does not exist.
2. The library file depends on something that cannot be found when the environment is not being controlled by Qt Creator.
3. The library file exists but is not a dynamically loadable library.

If you are saying that 1 does not apply then my money is on option 2. Given that you are afflicted with Windows then the problem is that whatever you are depending on is not in the system PATH. If it runs in the IDE then this quite likely a Qt library, but it could anything else you have added to the IDE run-time PATH.