[Lazarus] formatfloat negative zero (-0)

[Philippe]

if (Result<>'') and (Result[1]='-1') then begin 

maybe ( '-1' ->
'-' ) 

if (Result<>'') and (Result[1]='-') then begin 

? 

Em
07.07.2014 10:48, Dmitry Boyarintsev escreveu: 

> Will straight forward
solution work? how about this: 
> 
> unit MySysUtils; 
> 
> interface 
>

> uss SysUtils; 
> 
> // the function will cut heading "-" if all
digits in the number are zeros. 
> // it will leave the result unchanged
otherwise. 
> 
> function FormatFloat(const fmt: string; num: double):
string; 
> var 
> i : integer; 
> begin 
> Result:=
SysUtils.FormatFloat(fmt, num); 
> if (Result<>'') and (Result[1]='-1')
then begin 
> for i:=2 to length(Result) do 
> if Result[i] in
['1'..'9'] then Exit; 
> Result:=Copy(Result, 2, length(Result)-1); 
>
end; 
> 
> end; 
> .... 
> in your program. Put "MySysUtils" as the last
unit in the uses section (so your working unit would use MySysUtils
FormatFloat, instead of the implementation at SysUtils) 
> 
> thanks, 
>
Dmitry 
> 
> On Mon, Jul 7, 2014 at 5:00 PM, Andrea Mauri
<andrea.mauri.75 at gmail.com> wrote:
> 
>>>> using formatfloat function I
got an unexpected behaviour.
>>>> If I round negative numbers I can get
as result of formatfloat = '-0'.
>>>> I think it is a bug, since -0 has
no meaning, zero is zero.
>>>> How can I make a workaround?
>>>>
e.g.
>>>> label1.Caption:= FormatFloat('0.###',
strtofloat(edit1.Text));
>>>> if in edit1.text I have -0.000001 I got -0
as result while I would like to get 0.
>>>> 
>>>> Is it a bug, what can
I do?
>>> 
>>> Minus-zero is a recognized computational 'feature' of
floats on computers, not a bug (AFAIK).
>>> 
>>> The float variable
value of StrToFloat(edit1.text) is still -0.000001 though;
>>> (try
assigning it to a float type variable and watch it)
>> OK, I understand
that computationally -0 has meaning (since as you said the float
variable value of StrToFloat(edit1.text) is still -0.000001).
>> Anyway
It has no meaning for the final user of the application (at least for
any standard user of an application).
>> The final user does not care
that -0 has meaning for the computer.
>> e.g. I would like to represent
a float value with 3 decimal digits. I don't care of the remaining
digits, -0.000 has no meaning, it just means that there are some digits
(somewhere after the third decimal digits) that are not equal to zero
and that if they are considered the value is negative (but I don't want
to consider any digit after the third decimal one!).
>> Try to do it in
excel or libreoffice:
>> - write in a cell -0.00001 and set to 3 the
decimal digits, you got -0.000 or 0.000?
>> And you got the same results
using any software that deals with numbers.. 
>> 
>>> Does the same
happen if you Round() it to integer?
>>> e.g.
>>> label1.caption :=
Format('%d',[Round(strtofloat(edit1.text))]);
>>> (I know this isn't
what you're after
>> In this way I got 0.
>> Anyway I used as example
formatfloat since it has the same behaviour of
TFloatField.DisplayFormat, additionally DisplayFormat is a property that
is used to represent a formatted value to the final user (a human being
not a pc) for whom -0 has no meaning.
>> 
>> A.
> 
> --
>
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