FormatFloat possible improvement
lazarus / 64-FPC development

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bytebites · 2025-03-08 21:20

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i Function
FormatFloat(Const Format : String; Value : Extended; Const
FormatSettings: TFormatSettings) : String; Var  buf : Array[0..1024]
of Char;  Len: Integer; Begin  Len:=FloatToTextFmt(PChar(@Buf[0]),Valu
e,PChar(Format),FormatSettings);  Buf[Len]:=#0; 
Result:=StrPas(Pchar(@Buf[0]));End; 
Currently FormatFloat function uses StrPas to create result, is it
possible to use SetString instead since the length is known?

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ASerge · 2025-03-09 13:09

I suggest making it more safe:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
FormatFloat(const Format: string; Value: Extended; const
FormatSettings: TFormatSettings): string;   procedure
FormatCommon(Buf: PChar);  var    Len: SizeInt;  begin    Len :=
FloatToTextFmt(@Buf[0], Value, PChar(Format), FormatSettings);   
SetString(Result, Buf, Len);  end;   procedure FormatDynamicBuf;  var 
  Buf: PChar;  begin    Buf := GetMem(Length(Format) + 100);    try  
  FormatCommon(Buf);    finally      FreeMem(Buf);    end;  end; var 
Buf: array[Byte] of Char;begin  if Length(Format) < 100 then   
FormatCommon(Buf)  else    FormatDynamicBuf;end;
A simple test where the original gives an AV:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);var  LongFormat: string;begin 
Memo1.Text := FormatFloat('0000', 0.0, DefaultFormatSettings); 
LongFormat := StringOfChar('0', 2000); 
Memo1.Append(FormatFloat(LongFormat, 0.0, DefaultFormatSettings));end;

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AlexTP · 2025-03-09 14:38

@bytebites
I suggested the same in GitLab issue, without reading this topic.
https://gitlab.com/freepascal.org/fpc/source/-/issues/41181