sprintf in Delphi?

Question

Hi there!

Does anyone know a 100% clone of the C/C++ printf for Delphi? Yes, I know the System.Format function, but it handles things a little different.

For example if you want to format 3 to "003" you need "%03d" in C, but "%.3d" in Delphi.

I have an application written in Delphi which has to be able to format numbers using C format strings, so do you know a snippet/library for that?

Thanks in advance!

Answer 1

You could use the wsprintf() function from Windows.pas. Unfortunately this function is not declared correctly in the Windows.pas so here is a redeclaration:

function wsprintf(Output: PChar; Format: PChar): Integer; cdecl; varargs;
  external user32 name {$IFDEF UNICODE}'wsprintfW'{$ELSE}'wsprintfA'{$ENDIF};

procedure TForm1.FormCreate(Sender: TObject);
var
  S: String;
begin
  SetLength(S, 1024); // wsprintf can work only with max. 1024 characters
  SetLength(S, wsprintf(PChar(S), '%s %03d', 'Hallo', 3));
end;

Answer 2

Well, I just found this one:

function sprintf(S: PAnsiChar; const Format: PAnsiChar): Integer;
    cdecl; varargs; external 'msvcrt.dll';

It simply uses the original sprintf function from msvcrt.dll which can then be used like that:

procedure TForm1.Button1Click(Sender: TObject);
var s: AnsiString;
begin
  SetLength(s, 99);
  sprintf(PAnsiChar(s), '%d - %d', 1, 2);
  ShowMessage(S);
end;

I don't know if this is the best solution because it needs this external dll and you have to set the string's length manually which makes it prone to buffer overflows, but at least it works... Any better ideas?

Answer 3

If you want to let the function look more Delphi friendly to the user, you could use the following:

function _FormatC(const Format: string): string; cdecl;
const
  StackSlotSize = SizeOf(Pointer);
var
  Args: va_list;
  Buffer: array[0..1024] of Char;
begin
  // va_start(Args, Format)
  Args := va_list(PAnsiChar(@Format) + ((SizeOf(Format) + StackSlotSize - 1) and not (StackSlotSize - 1)));
  SetString(Result, Buffer, wvsprintf(Buffer, PChar(Format), Args));
end;

const // allows us to use "varargs" in Delphi
  FormatC: function(const Format: string): string; cdecl varargs = _FormatC;


procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage(FormatC('%s %03d', 'Hallo', 3));
end;

Answer 4

It's not recommended to use (ws)printf since they are prone to buffer overflow, it would be better to use the safe variants (eg StringCchPrintF). It is already declared in the Jedi Apilib (JwaStrSafe).