Question

I want to convert a large 64 bit value from decimal or hex string to 64 bit UINT64 data type. There is a UIntToStr to help converting the UINT64 to string, but no way to convert a 64 bit integer to a unsigned value, as a string. That means integer values greater than 2**63 can not be represented in decimal or hex, using the RTL. This is normally not a big deal, but it can happen that a user needs to input a value, as an unsigned integer, which must be stored into the registry as a 64 bit unsigned integer value.

procedure HandleLargeHexValue;

var
 x:UINT64;
begin

  x := $FFFFFFFFFFFFFFFE;

  try
  x := StrToInt('$FFFFFFFFFFFFFFFF'); // range error.
  except
    x := $FFFFFFFFFFFFFFFD;
  end;

  Caption := UintToStr(x);

end;

Update Val now works fine in Delphi XE4 and up. In XE3 and below Val(‘$FFFFFFFFFFFFFFFF’) works but not Val(‘9223372036854775899’). As Roeland points out below in Quality Central 108740: System.Val had problems with big UInt64 values in decimal until Delphi XE4.

Answer 1

UPDATE: In XE4 and later the RTL bug was fixed. This hack is only useful in Delphi XE3 or older

Well, if it ain’t there, I guess I could always write it.

(I wrote a pretty good unit test for this too, but its too big to post here)

unit UIntUtils;

{ A missing RTL function written by Warren Postma. }

interface
  function TryStrToUINT64(StrValue:String; var uValue:UInt64 ):Boolean;
  function StrToUINT64(Value:String):UInt64;

implementation

uses SysUtils,Character;

{$R-}

function TryStrToUINT64(StrValue:String; var uValue:UInt64 ):Boolean;
var
  Start,Base,Digit:Integer;
  n:Integer;
  Nextvalue:UInt64;
begin
  result := false;
  Base := 10;
  Start := 1;
  StrValue := Trim(UpperCase(StrValue));
  if StrValue='' then
    exit;
  if StrValue[1]='-' then
    exit;
  if StrValue[1]='$' then
  begin
    Base := 16;
    Start := 2;
    if Length(StrValue)>17 then // $+16 hex digits = max hex length.
        exit;
  end;
  uValue := 0;
  for n := Start to Length(StrValue) do
  begin
      if Character.IsDigit(StrValue[n]) then
          Digit := Ord(StrValue[n])-Ord('0')
      else if  (Base=16) and (StrValue[n] >= 'A') and (StrValue[n] <= 'F') then
          Digit := (Ord(StrValue[n])-Ord('A'))+10
      else
          exit;// invalid digit.

      Nextvalue := (uValue*base)+digit;
      if (Nextvalue<uValue) then
          exit;
      uValue := Nextvalue;
  end;
  result := true; // success.
end;

function StrToUINT64(Value:String):UInt64;
begin
  if not TryStrToUINT64(Value,result) then
    raise EConvertError.Create('Invalid uint64 value');

end;

end.