GetDiskFreeSpaceEx problems

Hello;

I am trying to create a function that will absorb all the free space that is available on a pc drive.

I am using GetDiskFreeSpaceEx.

The function like the one pasted below will nearly get all of the free space on my pc C: drive except 12.8 megs.

Also I turned off the option to automaticly call Disk Cleanup. As the Cleanup utility on Windows 98 automatically calls this up. But even with this option off it will still call up Disk Cleanup. Disk Cleanup utility gives the option to remove temporary internet files etc...

The sample below is a stripped down version of the actual code. The actual function is called repeatedly by a timer and creates multiple files up to 10 meg in size depending upon remaining disk space.

It works fine until it reaches 12.8 meg of free disk space left and quits.

The example below only creates one file but the code is basically the same.

Any comments or clues are apreciated.
RJ

int MyDialog::SqeezeDisk()
{
ULARGE_INTEGER fba, tnob;
GetDiskFreeSpaceEx(Drv,&fba,&tnob,NULL);

//Assign the free space available to this thread
unsigned _int64 Size = fba.QuadPart;

unsigned _int64 Wrote=0;
unsigned _int64 Sub=0;
char *ch;

MakeNewFileName(FileName);

FILE *fptr=NULL;
fptr=fopen(FileName,"wb");
if(fptr==NULL)
{
      MessageBox("ERROR failed to create file",FileName);
      return 1;
}//endif
//

////////////////////////WRITE FILE LOOP
unsigned _int64 x=0;

while(1)
{
   //Calculate largest size to write
      
      if(Size >= (unsigned _int64)10000)
            Sub=(unsigned _int64)10000;
      if(Size <  (unsigned _int64)10000 && Size >= (unsigned _int64)1000)
            Sub=(unsigned _int64)1000;
      if(Size <  (unsigned _int64)1000  && Size >= (unsigned _int64)100)
            Sub=(unsigned _int64)100;
      if(Size <  (unsigned _int64)100   && Size >= (unsigned _int64)10)
            Sub=(unsigned _int64)10;
      if(Size <  (unsigned _int64)10    && Size >= (unsigned _int64)1)
            Sub=(unsigned _int64)1;

      if(Size <=0)
      {
            flag=0;//not bad but done
            break; /////////ALL DISK SPACE IS USED UP SO BREAK!!!!
      }

      //create mem space to write
      ch = new char[Sub];

      //fill string with junk chars
      x=0;
      while(1)
      {
            ch[x]='z';
            x++;
            if(x==Sub)break;
      }//endwhile
      
      //write the string
      if(fwrite(ch,sizeof(char)*(int)Sub,1,fptr)<1) //was==-1
      {
            fclose(fptr);
            delete [] ch;
            return 1;
      }//endif

delete [] ch;
Wrote+=Sub;

//See if Wrote is same as or greater than free space
if((unsigned _int64)Wrote>=Size)break;

//recalculate free space
Size-=(unsigned _int64)Sub;

//check if done, no more space
if(Size<=(unsigned _int64)0)break;
}//endwhile
/////////////////////////END WRITE FILE LOOP

fclose(fptr);
//
return 0; //good
}//endfunc