Question

So, I am reading from ModBos over serial port and get readings something like the following : '+0020.8+0022.8-00.046-00.002-00.005-001.99+00.000+00.003';

Basically, there will always be 8 floating point readings, preceded by a plus or minus sign, although they may be of varying character length.

What’s the most efficient way to get the values an array of float (or array of string or TSringList)?

I am not certain, but this might be time critical, so efficiency probably has way over elegance.

Answer 1

I would do something like this:

type
  TFloatArray = array[0..7] of Double;

procedure ParseFloats(const aFloatStr: string;
  var aFloatArray: TFloatArray);
var
  lPos: Integer;
  lNextPos: Integer;
  lPosPositive: Integer;
  lPosNegative: Integer;
  i: Integer;
  lFormatSettings: TFormatSettings;
begin
  //do not forget formatsettings, or you will get problems with regional settings
  lFormatSettings.DecimalSeparator := '.';
  lFormatSettings.ThousandSeparator := ',';
  lPos := 1;
  for i := 0 to High(aFloatArray) do
  begin
    lPosPositive := PosEx('+', aFloatStr, lPos + 1);
    lPosNegative := PosEx('-', aFloatStr, lPos + 1);
    if lPosPositive = 0 then
      lNextPos := lPosNegative
    else if lPosNegative = 0 then
      lNextPos := lPosPositive
    else
      lNextPos := Min(lPosPositive, lPosNegative);
    if lNextPos = 0 then
      lNextPos := Length(aFloatStr) + 1;
    aFloatArray[i] := StrToFloat(Copy(aFloatStr, lPos, lNextPos - lPos), lFormatSettings);
    lPos := lNextPos;
  end;
end;

//call like this
var
  lFloats: TFloatArray;
begin
  ParseFloats('+0020.8+0022.8-00.046-00.002-00.005-001.99+00.000+00.003', lFloats);
end;

Because there are always 8 float values, a fixed array of 8 doubles is enough. I kept string manipulation to a minimum, only once per floating point value a string is copied. Important is the TFormatSettings, otherwise you will get errors on systems where the decimal separator is not a dot (like mine).

There is no exception handling here, I expect a string with 8 floating point values, nothing more, nothing less.