Thread: Heap Corruption when passing a vector of LPCWSTR's to a DLL.

Hi, sorry to trouble you again guys. Ok, this one is not a false alarm, I think.

The problem occurs when I want to pass a vector of LPCWSTR's (null-terminated wide strings) to a DLL. After I finished using the vector, it would crash with ........ error dialog:

This may be due to a corruption of the heap, which indicates a bug in photobooth.exe or any of the DLLs it has loaded.

the code:

Code:

std::vector<LPCWSTR> m_vPlaylist; //BAWE-20100301: NEW_VIDEOPLAYER. Used in to VideoPlayer (attractmovie.dll) .

Code:

bool InitLayer::createAttractWindow(
	SystemAccess* pSystemAccess,
	HMONITOR hMonitor
) {
	...
	// AttractWindow is a class from another DLL so in this case I passed the vector of LPCWSTR to another dll.

	m_pAttractWindow = AttractWindow::createInstance(
		hInstance,
		hMonitor,
		m_vPlaylist //BAWE-20100301: NEW_VIDEOPLAYER. Crash!!!
	);
	...
}

Code:

AttractWindow* AttractWindow::createInstance( HINSTANCE hInstance, HMONITOR hMonitor, std::vector<LPCWSTR> vPlaylist )
{
	...

	m_pVideoPlayer = new VideoPlayer( hWnd, true );

	m_pAttractWindow = new AttractWindow(
		hInstance,
		hWnd,
		pVideoPlayer
	);

	m_pAttractWindow->init( vPlaylist );
	...

	return m_pAttractWindow;
}

void AttractWindow::init(std::vector<LPCWSTR> vPlaylist) { 

	std::vector<LPCWSTR>::iterator iterPlaylist = vPlaylist.begin();


	while (iterPlaylist != vPlaylist.end() )
	{
		m_pVideoPlayer->AddMovie( *iterPlaylist ); 
		++ iterPlaylist;
	}
}

I've stepped through "AttractWindow::init" and it worked fine. But after I get to the last line of "AttractWindow::createInstance" (the "return m_pAttractWindow" line), it crashed. Why did this happen? Thanks in advance.

vector + DLL boundary = bad.

Best practice is to not pass anything across a DLL boundary that is not compatible with C.
You can pass the address of element zero of a vector to a DLL as an alternative when you just need to make the data visible inside the DLL. This isn't enough in your case though. You'll likely have to perform the memory allocation manually inside the DLL and not use a vector.

In any case, you can not pass a vector by reference to anything where you wish to modify it. That's what references are for. Again though, references do not exist in C, so they are also something that by best practices should not be used across DLL boundaries.

Well, I don't intend to change the values of the vector but I need to pass a set of values to the DLL. So as far as I concerned, it can be a "const std::vector<LPCWSTR> &" if needed. Any other solution?

EDIT: LoL!!! As a matter of fact using "const std::vector<LPCWSTR> &" works. The crash is gone now. Why didn't I think of that in the first place? Thanks for the hint iMalc.

http://msdn.microsoft.com/en-us/library/ms235460.aspx
http://support.microsoft.com/kb/172396

gg