Concept of threads when running a project in Qt

[Ahti]

Hi
I am working on project that needs to initialize COM library. I have copy pasted the code for that into my qt project .

COM Initialization code :

hres =  CoInitializeEx(0, COINIT_MULTITHREADED);  
if (FAILED(hres)){
     cout << "Failed to initialize COM library. Error code = 0x" << hex << hres << endl;
      return 1;      
 }

But when I run my project I get this error: Failed to initialize COM library. Error code = 0x80010106. I googled the error code and it reflects to this RPC_E_CHANGED_MODE. So after reading about when is ConInitializeEx returning this error and it turns out it has to something to do with threads. As being a newbie to Qt I know nothing about Qt threads.

Can anyone explain me what is going on ? and how to fix it ?

[jsulm]

@Ahti This is from the link you posted:
"A previous call to CoInitializeEx specified the concurrency model for this thread as multithread apartment (MTA). This could also indicate that a change from neutral-threaded apartment to single-threaded apartment has occurred. "
Did you call CoInitializeEx already before with other parameters? Did you create any threads in your app?

[Ahti]

@jsulm No I didn't called it before that is the only time I am calling that function. And no I didn't created any thread morever I don't know if qt creates thread on its own when running the project/application. The movement I run my project/application qt displays the app window and then closes it immediately.

[jsulm]

@Ahti said in Concept of threads when running a project in Qt:

closes it immediately.

Does it close if you don't call CoInitializeEx?

[Ahti]

@jsulm No it doesn't close if I don't call CoInitializeEx.

[jsulm]

@Ahti Did you try to use CoInitializeEx in a non Qt project to see how it behaves?

[Ahti]

@jsulm and what is non qt project ? Can you give example

[jsulm]

@Ahti said in Concept of threads when running a project in Qt:

and what is non qt project

Well, a C++ project which does not use Qt at all?
QtCreator even can create one.

[Ahti]

@jsulm visual studio ?

[jsulm]

@Ahti Why Visual Studio? You can use QtCreator or even a text editor to create plain C++ projects.