C / C++ / MFC

#include <fstream.h>
   ...
   char buffer[100];
   ifstream myFile ("data.bin", ios::in | ios::binary);
   myFile.read (buffer, 100);
   if (!myFile) {
       // An error occurred!
       // myFile.gcount() returns the number of bytes read.
       // calling myFile.clear() will reset the stream state
       // so it is usable again.
   }
   ...
   if (!myFile.read (buffer, 100)) {
       // Same effect as above
   }</fstream.h>

BOOL CFreeCluster::GetBitmap()
{
	STARTING_LCN_INPUT_BUFFER StartingLCN;
	VOLUME_BITMAP_BUFFER *Bitmap = NULL;
	ULONGLONG BitmapSize;
	DWORD BytesReturned;
	BOOL Result;

	StartingLCN.StartingLcn.QuadPart = 0;

	// Allocate buffer
	// Call FSCTL_GET_VOLUME_BITMAP once with a very small buffer
	// This will leave the total number of clusters in Bitmap->BitmapSize and we can
	// then correctly allocate based off that
	// I suppose this won't work if your drive has only 40 clusters on it or so :)
	BitmapSize = sizeof (VOLUME_BITMAP_BUFFER) + 4;
	Bitmap = (VOLUME_BITMAP_BUFFER *) malloc (BitmapSize);
	HANDLE hHandle=OpenDrive();

	Result = DeviceIoControl
		(
		hHandle,
		FSCTL_GET_VOLUME_BITMAP,
		&StartingLCN,
		sizeof (StartingLCN),
		Bitmap,
		BitmapSize,
		&BytesReturned,
		NULL
		);

	// Bad result?
	if (Result == FALSE  &&  GetLastError () != ERROR_MORE_DATA)
	{
		//wprintf ("\nDeviceIoControl returned false, GetLastError() was not ERROR_MORE_DATA\n");
		free (Bitmap);
		return (false);
	}

	// Otherwise, we're good
	//BitmapSize = sizeof (VOLUME_BITMAP_BUFFER) + (Bitmap->BitmapSize.QuadPart / 8) + 1;
	BitmapSize = (Bitmap->BitmapSize.QuadPart / 8) + 1;
	int nBufferSize=8*512*3;//3 cluster at a time
	ULONGLONG ullItr=BitmapSize/nBufferSize;
	
	if(BitmapSize%nBufferSize!=0)
		ullItr++;

	Bitmap = (VOLUME_BITMAP_BUFFER *) realloc (Bitmap, nBufferSize+1);

	ULONGLONG ullClusterNo=0;
	for (ULONGLONG ullTmp=0; ullTmp < ullItr; ullTmp++)
	{
		if(BitmapSize < nBufferSize)
			nBufferSize=BitmapSize;

		memset(Bitmap->Buffer,0x0,nBufferSize+1);
		StartingLCN.StartingLcn.QuadPart=ullTmp*nBufferSize;
		//Bitmap->StartingLcn.HighPart=ullTmp*nBufferSize;

		
		//StartingLCN.StartingLcn.LowPart=2560;//ullTmp*nBufferSize;
		//StartingLCN.StartingLcn.HighPart=2560+nBufferSize;//ullTmp*nBufferSize;
		//Bitmap->BitmapSize.LowPart=2560;
		
		//Bitmap->StartingLcn.QuadPart=ullTmp*nBufferSize;
		Result = DeviceIoControl
			(
			hHandle,
			FSCTL_GET_VOLUME_BITMAP,
			&StartingLCN,
			nBufferSize,//sizeof (StartingLCN),
			Bitmap,
			nBufferSize,
			&BytesReturned,
			NULL
			);
		int p=GetLastError();

		if (Result == FALSE  &&  GetLastError () != ERROR_MORE_DATA)
		{
			//wprintf ("\nDeviceIoControl returned false, GetLastError() was not ERROR_MORE_DATA\n");
			free (Bitmap);
			return (false);
		}

		BitmapSize=BitmapSize-nBufferSize;
       }

	return (true);
}