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How comes this code leaks memory?

Julian Watzinger · 2013-05-15T14:42:37

Hello, I've come across one rather strange kind of memory leak. I always thought memory leaks where caused if you forget to delete a resource you allocated, or loose a pointer to it, but this one... well, look: void Text::Draw(render::Stage& stage, const math::Rect& rect, LPCWSTR lpText, DWORD dFlags, float f) { math::Rect r(rect); r.width += rect.x; r.height += rect.y; /* Leak: */ delete m_pCall; m_pCall = new render::DrawFont(m_pActiveFont->GetAclFont().m_lpFont, lpText, r.GetWinRect(), dFlags, m_color.GetD3DColor()); /* End Leak */ m_pInstance->SetCall(*m_pCall); stage.SubmitInstance(*m_pInstance); } So, those two lines cause the leak. If I draw some text using this (unoptimized, hackaround-like) font rendering method for my renderer, memory used by the application will rise continously in small amounts noticable in the task manager. Here is how my DrawFont-method is declared: class DrawFont : public DrawCall { public: DrawFont(const LPD3DXFONT font, const std::wstring& stText, const RECT& rect, DWORD flags, D3DCOLOR color): stText(stText), font(font), rect(rect), flags(flags), color(color) { type = Font; } void Execute(const DX9Device& device) const { RECT r(rect); font->DrawTextW(nullptr, stText.c_str(), stText.size(), &r, flags, color); } private: RECT rect; DWORD flags; std::wstring stText; D3DCOLOR color; const LPD3DXFONT font; }; Now uhm... I don't really see any reason why this could leak memory. I'm deleting the draw call I allocated before, I'm not newing anything in between those two actions concerning the DrawFont-class, and the general render interface doesn't show this leaking behaviour, its only the text-class. Also it has nothing to do with calling the "Execute"-function, even if I comment out the part in my render queue where this call is processed, it still leaks. As soon as I comment out that two lines, no such rise in memory. Am I really that stupid, or is there some good reason why memory usage could rise by those simple actions and/or something I missed out?

General and Gameplay Programming Programming

Started by Juliean May 15, 2013 01:30 PM

9 comments, last by Juliean 10 years, 11 months ago

Juliean

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May 15, 2013 02:42 PM

Thanks all for the additional explanation!

You realise that looking at the memory in the task manager is not a good indication to check if a memory leak is present. Install Valgrind or Visual Leak Detector to make sure you really have a memory leak or not. A never ending recursive function would show the same thing in task explorer until it hits the stack limit and then it will crash.

Yeah, sure, I wasn't even looking for a memory leak, I just happened to be looking at the task manager the right time and noticed that rise in memory. Turned out well this time, surely if I was really going after memory leaks I'd check out a tool for that case, thanks for the hints. Still, a endloss loop or recursive function is out of the question for this case, since, well, the the app was still running (no threads), and normally such a function would cause the app to die almost instantly (at least started with Debugger from Visual Studio), so I don't think its that bad as a general sign of some sort of memory related problem...

How comes this code leaks memory?

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How comes this code leaks memory?

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