QPluginLoader instance always returns null

[meysam_hashemi]

QT_BEGIN_NAMESPACE and QT_END_NAMESPACE should not be needed in the header.

When loading, is plugin or deviceManager NULL? If plugin is NULL then the plugin DLL is either not found at all, or unable to load. If deviceManager is NULL (and plugin is not) then the loaded plugin does not contain a QObject handling the interface.
Are you certain the Device-Manager.dll is in the location identified pluginPath?
Are all of the external runtime dependencies of the plugin DLL met in the environment in which it is running? That is, if Device-Manager.dll depends on foolib.dll is that in the PATH?

Thanks for reply. The plugin is in correct path and pluginLoader is not null but instance() return null. I think that one of run-time dependencies is missing or something. I'm breaking the code to several part and testing it to find out what exactly is wrong!

[meysam_hashemi]

I found the reason but i have no idea why it cause the problem, Im using library that is linked to project but when i use its function, The instance returns null.

LIBS += $$(STANDARD_XFS_DIRECTORY)/LIB/MSXFS.lib
INCLUDEPATH += $$(STANDARD_XFS_DIRECTORY)/INCLUDE

LIBS += $$(STANDARD_XFS_DIRECTORY)/LIB/MSXFS.lib
INCLUDEPATH += $$(STANDARD_XFS_DIRECTORY)/INCLUDE

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Can anyone tell me why it happens?

[high_flyer]

mixed build mode perhaps? (release/debug)

[meysam_hashemi]

mixed build mode perhaps? (release/debug)

No, Both are in debug!
The thing is, I did something exactly like this before with CMakeList.txt and Visual Studio but its not working with MinGW and QT Creator . I'm missing something but i have no idea what it is !!!

---

Added after 18 minutes:

The following configs of library and plugin in `CMakeList.txt` work perfectly fine when i make the project with `Visual Studio`. (Made with CMake)

ADD_DEFINITIONS(${QT_DEFINITIONS})																						
    ADD_DEFINITIONS(-DUNICODE -D_UNICODE)																						
    ADD_DEFINITIONS(-DQT_PLUGIN)																				
    ADD_DEFINITIONS(-DQT_SHARED)																							
    ADD_DEFINITIONS(-DQT_DLL)																							
    ADD_DEFINITIONS(-DQT_LARGEFILE_SUPPORT)
    ADD_DEFINITIONS(-DQT_THREAD_SUPPORT)
 
    INCLUDE_DIRECTORIES(
    	${STANDARD_XFS_DIRECTORY}/INCLUDE
    )
 
    LINK_DIRECTORIES(
    	${STANDARD_XFS_DIRECTORY}
    	${STANDARD_XFS_DIRECTORY}/LIB
    )
 
    SET(XFS_LIBS
    	MSXFS
    	xfs_conf
    	SSIDLL
    )
 
    TARGET_LINK_LIBRARIES(Device-Manager 
    	${XFS_LIBS}
    )

ADD_DEFINITIONS(${QT_DEFINITIONS})																						
    ADD_DEFINITIONS(-DUNICODE -D_UNICODE)																						
    ADD_DEFINITIONS(-DQT_PLUGIN)																				
    ADD_DEFINITIONS(-DQT_SHARED)																							
    ADD_DEFINITIONS(-DQT_DLL)																							
    ADD_DEFINITIONS(-DQT_LARGEFILE_SUPPORT)
    ADD_DEFINITIONS(-DQT_THREAD_SUPPORT)

    INCLUDE_DIRECTORIES(
    	${STANDARD_XFS_DIRECTORY}/INCLUDE
    )
    
    LINK_DIRECTORIES(
    	${STANDARD_XFS_DIRECTORY}
    	${STANDARD_XFS_DIRECTORY}/LIB
    )
    
    SET(XFS_LIBS
    	MSXFS
    	xfs_conf
    	SSIDLL
    )
    
    TARGET_LINK_LIBRARIES(Device-Manager 
    	${XFS_LIBS}
    )

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And this is the configs of library and plugin in `.pro` file in `Qt Creator` with `MinGW` which is not working when i use the library.

QT  -= gui
    QT  += core sql
 
    TARGET = Device-Manager
    TEMPLATE = lib
    CONFIG += plugin
    CONFIG += c++11
 
    DEFINES += DEVICEMANAGER_LIBRARY
 
    INCLUDEPATH += $$(STANDARD_XFS_DIRECTORY)
    INCLUDEPATH += $$(STANDARD_XFS_DIRECTORY)/INCLUDE
    message(Include : $${INCLUDEPATH})
 
    LIBS += $$(STANDARD_XFS_DIRECTORY)/SSIDLL.lib
    LIBS += $$(STANDARD_XFS_DIRECTORY)/LIB/MSXFS.lib
    LIBS += $$(STANDARD_XFS_DIRECTORY)/LIB/xfs_conf.lib
    message(Lib : $${LIBS})

QT  -= gui
    QT  += core sql
    
    TARGET = Device-Manager
    TEMPLATE = lib
    CONFIG += plugin
    CONFIG += c++11
    
    DEFINES += DEVICEMANAGER_LIBRARY
    
    INCLUDEPATH += $$(STANDARD_XFS_DIRECTORY)
    INCLUDEPATH += $$(STANDARD_XFS_DIRECTORY)/INCLUDE
    message(Include : $${INCLUDEPATH})
    
    LIBS += $$(STANDARD_XFS_DIRECTORY)/SSIDLL.lib
    LIBS += $$(STANDARD_XFS_DIRECTORY)/LIB/MSXFS.lib
    LIBS += $$(STANDARD_XFS_DIRECTORY)/LIB/xfs_conf.lib
    message(Lib : $${LIBS})

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So i can say the code it self is fine and i'm definitely missing some configs in `.pro` file.

PS1: Plugin and the application that load the plugin, Both have `INCLUDEPATH` and `LIBS` of the library in their pro file.

PS2: The application and the plugin both are in debug mode

PS3: I dont get any compile error or linker error during compile.

[high_flyer]

No, Both are in debug!

do you have any other 3rd party dependencies which might be in release?

I'd try to build your project in release and try to see if it works, its an easy test worth trying.

[meysam_hashemi]

do you have any other 3rd party dependencies which might be in release?

I'd try to build your project in release and try to see if it works, its an easy test worth trying.

No man i dont

I made simple console application and included my library header and lib file and called the function and this is the error i get when i run the application. So it must be it. But seriously why!!!

The Code:

LPWFSRESULT result = new WFSRESULT();
WFSFreeResult(result)

LPWFSRESULT result = new WFSRESULT();
WFSFreeResult(result)

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mingw.jpg

[high_flyer]

Is this typo 'DeviceMAnager' really in the code or only in the code posted here?:

if (plugin)
{
    deviceManager = qobject_cast<DeviceMAnager *>(plugin);
    return true;
}

if (plugin)
{
    deviceManager = qobject_cast<DeviceMAnager *>(plugin);
    return true;
}

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I'd add some defencive code here:

QPluginLoader * pluginLoader = new QPluginLoader(pluginPath.c_str());
QObject * plugin = pluginLoader->instance();
 
if (plugin)
{
    deviceManager = qobject_cast<DeviceMAnager *>(plugin);
    if(deviceManager) return true;
    return false;;
}
else
{
    delete pluginLoader;
    return false;
}

QPluginLoader * pluginLoader = new QPluginLoader(pluginPath.c_str());
QObject * plugin = pluginLoader->instance();

if (plugin)
{
    deviceManager = qobject_cast<DeviceMAnager *>(plugin);
    if(deviceManager) return true;
    return false;;
}
else
{
    delete pluginLoader;
    return false;
}

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[ChrisW67]

Your screenshot clearly shows error 0xc0000135, which means STATUS_DLL_NOT_FOUND. This goes back to:

Are all of the external runtime dependencies of the plugin DLL met in the environment in which it is running? That is, if Device-Manager.dll depends on foolib.dll is that in the PATH?

Is the MSXFS.DLL in the run time PATH of the process or in the same directory as the plugin DLL? Is everything the MSXFS.DLL depends on also in one of those locations?

[meysam_hashemi]

Your screenshot clearly shows error 0xc0000135, which means STATUS_DLL_NOT_FOUND. This goes back to:

Is the MSXFS.DLL in the run time PATH of the process or in the same directory as the plugin DLL? Is everything the MSXFS.DLL depends on also in one of those locations?

Yes.

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Well, I found the problem however its so silly. I run project over windows 10 32 bit and it work fine. Maybe something is not incompatible with 64 bit and that caused this mess.

Thanks everyone for all your solution and i hope your solutions help others problem.

Thanks alot!