How to display a floating point value as scientific parameter in Delphi

Question

We have a frequent need to display floating point values in a scientific form with multiplier and units, for example the value of 1500 V (volts) would be displayed as 1.5 kV. A very small voltage of 1e-4 V would be displayed as 100 uV. For years we've used an internally created routine to make this float to string conversion but I was minded to wonder recently whether such a means was more generally available?

Answer 1

If your goal is to make your routines more "native", you could take a look at the ConvUtils and StdConvs units and see if you could base your routines on the conversion functions offered by these units. (Not sure when those units were introduced. Quick google search suggest Delphi 6)

But that won't necessarily achieve much for you. (Depending on what you are looking to achieve)

Answer 2

I'm using this FormathWithPrefix function with little knowledge about logarithms... :)

Support SI prefixes range!

function FormathWithPrefix(n: double; decimals: integer): string;
var
  index: integer;
const
  Prefixes: array[-9..9]of string = ('<', 'y', 'z', 'a', 'f', 'p', 'n', 'µ', 'm', '',
    'k','M', 'G', 'T', 'P', 'E', 'Z', 'Y', '>');   
begin
  index := round((Ln(n) / Ln(10) - 1) / 3);
  if index > 9 then 
    index := 9;
  if index < -9 then 
    index := -9;
  result := (FloatToStrF(n / Exp(index * 3 * ln(10)) , ffFixed, 20, decimals) + Prefixes[index]);
end;

begin
  n := 1500;
  Writeln(FormathWithPrefix(n, 1),'V');

Answer 3

Try here: http://www.delphibasics.co.uk/RTL.asp?Name=FloatToStrF

Particularly this one: `ShowMessage('Using 8,4 = '+FloatToStrF(amount1, ffFixed, 8, 4)); would indicate you can use something like this:

var 
  Answer:string;    
  thevolts:double;
begin
  Answer:= FloatToStrF(thevolts, ffFixed, 8, 4)+' kV'
end;