Question

just curious why the following code fails to convert uint64 value in string representation ?

var
  num: UInt64;
  s: string;
  err: Integer;

begin
  s := '18446744073709551615';  // High(UInt64)
  Val(s, num, err);
  if err <> 0 then
    raise Exception.Create('Failed to convert UInt64 at ' + IntToStr(err));  // returns 20
end.

Delphi XE2

Am I missing something here ?

Answer 1

According to the documentation,

S is a string-type expression; it must be a sequence of characters that form a signed real number.

I agree the documentation is a bit vague; indeed, what exactly does form mean, and exactly what is meant by a signed real number (especially if num is an integer type)?

Still, I think the part to highlight is signed. In this case, you want an integer, and so S must be a sequence of characters that form a signed integer. But then your maximum is High(Int64) = 9223372036854775807