Hi, I'm passing a pointer buffer as void * to a C library that returns Uint8 or Uint16 (and signed types).

If I explicitly declare the buffer as PByte, PWord, etc. I get exactly what I need, but, I would like to work with an abstract type (for example Pointer) and cast it depending on a flag returned by the library.

If I pass a Pointer (instead of a PWord or PByte) and cast it to PWord, for example. I get the same result if I have passed a PByte.

How can I handle a situation like this without explicitly define each type?.

Regards,

I'm not sure what you mean. How does your code look like now, and how do you want it to look?

You can modify the function declarations in your units, to accept the properly typed pointer or an Var parameter.

DoDi

If you mean overloading functions, that is exactly what I don't want to do.

My methods are similar to this:

procedure TImageDrawer.Draw(ABuffer: PWord);
begin
  ...
end;

As you can see, I'm passing a PWord, this works as expected, the same if I modify the funcion passing a PByte. But, as I cannot create a new function for each pointer type, I would like to pass a generic pointer, and typecast it inside the function, for example:

procedure TImageDrawer.Draw(ABuffer: Pointer);
begin
  ...
  if MyImage.DataType = "Uint16" then
    data = PWord(ABuffer)^
  else
  if MyImage.DataType = "Uint8" then
    data = PByte(ABuffer)^;
end;

If I do this, the result of PWord(ABuffer) is the same as PByte(ABuffer). I'm starting to think PByte is equal to Pointer type.

The address of ABuffer stays the same, the typecasts only affect the element type (pointed to).

I cannot provide a simpler solution than you found already. You have to find an type for "data" that allows for both signed and unsigned values in the range of the values, too, e.g. Int64. When ABuffer contains multiple values, typecasts also are required when incrementing the pointer.

DoDi

What is "data"?

PPointerCast=^TPointerCast
TpointerCast=record
case integer of
0:(pb:PByte);
1:(pw:PWord);
2:(pd:PDword);
3:(pu:PtrUint);
4:(pi:PtrInt);
end;
function some_function(ptr:TPointerCast):boolean;

regards,
Anton