What's wrong with my std::ostringstream usage

Tried to my update my window title with some performance metrics for my vulkan renderer with std::ostringstream. When i run it tells there's access violattion leading to xtring file funtion size_t length(_In_z_ const _Elem* const _First) where the the _First parameter is null as shown on picture below. Here's the code i wrote

Code:

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void ApplicationBaseVk::UpdatePerformanceMatrics()
{
        std::ostringstream osstream;
        osstream << mWindowTitle << " Frametime : " << mDeltaTime << " FPS : " << 1.0f / mDeltaTime;

        glfwSetWindowTitle(mWindow, osstream.str().c_str());
}

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Attachment 36049
Or maybe i've done in wrong way.I'm running latest msvc 2022.Sorry for my bad english.Thank you

Update: I tried on simple console app and it works fine.This confusing me.

Code:

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#include <iostream>
#include <sstream>

int main()
{
    int i = 0;
    std::ostringstream ss;
    ss << "Hello" << i << "\n";

    std::cout << ss.str().c_str();
}

---

Attachment 36050

Update : It turns out I forgot to do

Code:

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mWindowTitle = appName;

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in my app initialization function.Foolish me. Sorry for the trouble. Have a nice day folks.

We've all made stupid mistakes at least once, twice...