Rtrim in array

Recently i used a dll file which needed array of bytes for input
i got 512000 bytes in this way:

ReDim buffer(512000) As Byte

and gave it to .dll file .
but .dll file only used some of it for example 200000 byte.
everytime .dll file use different space so how much it use my array is unknown.
how can i free extra memory from end of my array??
i copied my array to a string and use Rtim for it but it didnt work.

plz help
thanks anyway!!!

The DLL has to tell you how much memory it used. Then you can begin your own memory management.

Unfortunetly it doesnt tell anything.
is there anyway???

thanks again

Well how do you know its not using all the memory?