Du läser för närvarande dokumentationen för:
ECF_CalculateFreeSpace
The ECF_CalculateFreeSpace function calculates the amount of free disk space on a mounted filesystem.
ECF_ErrorCode ECF_CalculateFreeSpace(
   char cDriveLetter,
   DWORD *pdwFreeSectors,
   WORD *pwSectorSize
);
Parameters
cDriveLetter
This is the drive letter of the file system you which to calculate the free space of. E.g. 'A'
pdwFreeSectors
This is a pointer to a DWORD that will receive the number of free sectors.
pwSectorSize
This is a pointer to a WORD that will receive the sector size. This parameter is not mandatory and may be NULL.
Return value
Returns one of the ECF error codes (ECFERR_SUCCESS on success)
Remarks
ECF_CalculateFreeSpace needs to scan the entire FAT table to get an accurate count of the number of free sectors which may take some time.