You've to specify in DECLARE that those parameter're passed by reference, properly initialize them and pass by reference to the function.

DECLARE LONG GetDiskFreeSpace IN kernel32 ;
	STRING, LONG @, LONG @, LONG @, LONG @
LOCAL ret, strDrive, lngSectors, lngBytes, lngFreec, lngTotalc
STORE 0 TO lngSectors, lngBytes, lngFreec, lngTotalc
ret = GetDiskFreeSpace(strDrive, @lngSectors, @lngBytes, @lngFreec, @lngTotalc)
? ret, lngSectors, lngBytes, lngFreec, lngTotalc

The function GetDiskFreeSpace has a bug. See faq #7847 for to how get correct info.

>Hi All!
>How come when I use this API call, the last 4 parameters aren't being returned in VFP? I've tried it in VB and it works fine (giving me the sectors per cluster, bytes per cluster, free clusters and total number of clusters). I declared it as such:
>
>DECLARE LONG GetDiskFreeSpace IN kernel32.dll STRING, LONG, LONG, LONG, LONG
>
>and called it like so:
>
>LOCAL ret, strDrive, lngSectors, lngBytes, lngFreec, lngTotalc
>ret = GetDiskFreeSpace(strDrive, lngSectors, lngBytes, lngFreec, lngTotalc)
>
>ret evaluates to a non-zero which means the call was successful, but how come I don't get any return values that the function should return?
>
>In VFP, how do you go about declaring an API call, and calling it? Especially those API calls that contain more than one parameter and returns more than one variable? Thanks.