Converting TMemoryStream to 'String' in Delphi 2009

Question

We had the following code prior to Delphi 2009:

function MemoryStreamToString(M : TMemoryStream): String;
var
    NewCapacity: Longint;
begin
    if (M.Size = > 0) or (M.Memory = nil) then
       Result:= '' 
    else
    begin
       if TMemoryStreamProtected(M).Capacity = M.Size then
       begin
           NewCapacity:= M.Size+1;
           TMemoryStreamProtected(M).Realloc(NewCapacity);
       end;
       NullString(M.Memory^)[M.Size]:= #0;
       Result:= StrPas(M.Memory);
    end;
end;

How might we convert this code to support Unicode now with Delphi 2009?

Answer 1

The code you have is unnecessarily complex, even for older Delphi versions. Why should fetching the string version of a stream force the stream's memory to be reallocated, after all?

function MemoryStreamToString(M: TMemoryStream): string;
begin
  SetString(Result, PChar(M.Memory), M.Size div SizeOf(Char));
end;

That works in all Delphi versions, not just Delphi 2009. It works when the stream is empty without any special case. SetString is an under-appreciated function.

If the contents of your stream aren't changing to Unicode with your switch to Delphi 2009, then you should use this function instead:

function MemoryStreamToString(M: TMemoryStream): AnsiString;
begin
  SetString(Result, PAnsiChar(M.Memory), M.Size);
end;

That's equivalent to your original code, but skips the special cases.