Jump to content
  • Advertisement
Sign in to follow this  
Naked Shooter

Problem initializing object

This topic is 2226 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi! I have an abstract GameOS object, and a windows implementation in WindowsOS.


class GameOS
{
private:
bool fullScreen;
public:
virtual void showWindow() = 0;
virtual void resize(U32 width, U32 height) = 0;
virtual void initialize() = 0;
virtual void processOSMessages()=0;
virtual void shutdown()=0;
virtual void setFullScreen(bool value) = 0;
};


I also have a platform detection class, where I try to allocate an OS object. For each platform, the platform detection class would use different cpp files. I was playing around with a custom stack allocator, trying to allocate the OS from a big stack that's passed in:


class PlatformDetection
{
private:

public:
PlatformDetection();
~PlatformDetection(void);


static GameOS* initAndReturnOS(StackAllocator& subsystemStack);
};


The windows implementation of the the initAndReturn function looks like this:


GameOS* PlatformDetection::initAndReturnOS(StackAllocator& subsystemStack)
{
WindowsOS* ret = (WindowsOS*)subsystemStack.allocateAligned(sizeof(WindowsOS), __alignof(WindowsOS));
memset(ret, 0, sizeof(WindowsOS));
ret->initialize();
return (GameOS*)ret;
}


The program crashes on ret->initialize(). The thing is, when I comment out "virtual void initialize() = 0;" in GameOS.h, it behaves normally, so it looks like it's trying to call an undefined function of GameOS rather than WindowsOS's function, even though the point is of type WindowsOS*...

Does anyone know why this is?

Share this post


Link to post
Share on other sites
Advertisement
When you call memset(ret,0,sizeof(WindowsOS)); you might be trashing the vtable. If initialize is not a virtual function, then ret->initialize() doesn't need the vtable to be called, so it doesn't crash. I am curious as to why you used memset to clear that object.

Share this post


Link to post
Share on other sites

When you call memset(ret,0,sizeof(WindowsOS)); you might be trashing the vtable. If initialize is not a virtual function, then ret->initialize() doesn't need the vtable to be called, so it doesn't crash. I am curious as to why you used memset to clear that object.


The memset was basically there for no reason, I thought it might help but it didn't..

The solution was to use a 'placement new' like this:


WindowsOS* ret = (WindowsOS*)subsystemStack.allocateAligned(sizeof(WindowsOS), __alignof(WindowsOS));
ret = new (ret) WindowsOS;


This way, we can properly construct an object wile using a pre-allocated chunk of memory to store it. Edited by Naked Shooter

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!