[Qt-interest] Cutting useless decimal places

[Karl Krach]

Hello Atlant,

I don't know if my translation into English is correct, but in physics 
you differ between
  * valid digits and
  * decimal places.

You have implemented '4 valid digits'. This would be ok for me, but 
better would be if Qt would provide me some function which just removes 
all 'unneeded zeros' on the right.

      0.000125346     -> 0.000125346
      0.001253457     -> 0.001253457
      0.012534568     -> 0.012534568
      0.125345679     -> 0.125345679
      1.253456789     -> 1.253456789
      12.534567890    -> 12.53456789
      125.345678900   -> 125.3456789
      1253.456789000  -> 1253.456789
      12534.567890000 -> 12534.56789
      12534.567800000 -> 12534.5678
      12534.567000000 -> 12534.567
      12534.560000000 -> 12534.56
      12534.500000000 -> 12534.5
      12534.510000000 -> 12534.51
      12534.000000000 -> 12534

but also

      5.000000000     -> 5
      5.000100000     -> 5.0001

Maybe I will create something like this:

QString float2string(float number)
{
	return QString("%1").arg( number, 0, 'f' )
                             .remove( QRegExp("\\.?0*$") );
}

original:  "200.000000"
new:       "200"
original:  "20.000000"
new:       "20"
original:  "0.500000"
new:       "0.5"
original:  "0.125000"
new:       "0.125"
original:  "7000.000000"
new:       "7000"


Thanks,

Charly


On 10/25/2010 01:56 PM, Atlant Schmidt wrote:
> Charly:
>
>    Here's something to get you started / help us all
>    think about your question.
>
>    This produces the following output:
>
>      0.000125346 ->  0.000
>      0.001253457 ->  0.001
>      0.012534568 ->  0.013
>      0.125345679 ->  0.125
>      1.253456789 ->  1.253
>      12.534567890 ->  12.54
>      125.345678900 ->  125.3
>      1253.456789000 ->  1253
>      12534.567890000 ->  12535
>      12534.567800000 ->  12535
>      12534.567000000 ->  12535
>      12534.560000000 ->  12535
>      12534.500000000 ->  12534
>      12534.510000000 ->  12535
>      12534.000000000 ->  12534
>      602214178999999989284864.000000000 ->  602214178999999989284864
>
>                   Atlant
>
>
> #include<stdio.h>
> #include<math.h>
>
>
> // Forward routines
> //
>
> int  main(int argc, char **argv);
> void try_one( double input );
>
>
> int main(int argc, char **argv)
>    {
>
>      try_one( 0.0001253456789 );
>      try_one( 0.001253456789 );
>      try_one( 0.01253456789 );
>      try_one( 0.1253456789 );
>      try_one( 1.253456789 );
>      try_one( 12.53456789 );
>      try_one( 125.3456789 );
>      try_one( 1253.456789 );
>      try_one( 12534.56789 );
>      try_one( 12534.5678 );
>      try_one( 12534.567 );
>      try_one( 12534.56 );
>      try_one( 12534.5 );
>      try_one( 12534.51 );
>      try_one( 12534.0 );
>      try_one( 6.02214179E23 );
>
>      return 0;
>
>    }
>
>
> void try_one( double input )
>    {
>
>      double output;
>      double absval;
>
>      output = round(input*1000.0)/1000.0;
>      absval = fabs( output );
>
>      if      (absval<   10.0)
>          printf( "%.9f ->  %.3f\n", input, output );
>      else if (absval<  100.0)
>          printf( "%.9f ->  %.2f\n", input, output );
>      else if (absval<1000.0)
>          printf( "%.9f ->  %.1f\n", input, output );
>      else
>          printf( "%.9f ->  %.0f\n", input, output );
>
>    }
>
>
>
> -----Original Message-----
> From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of mailinglists at bluespirit.la
> Sent: Monday, October 25, 2010 04:04
> To: qt-interest at trolltech.com
> Subject: [Qt-interest] Cutting useless decimal places
>
> Hello,
>
> a very simple question: How can I create a QString from a
> float/double, in format 'f' without giving a explicit number of decimal
> places to the arg() arguments?
>
> qDebug()<<  QString("Hello world: %1").arg( fNumber, 0, 'f' );
>
> When setting fNumbers to '0.125' I want an output of '0.125'. But when
> setting the fNumbers variable to '200', I don't want an output of
> "200.000". I want also use the localized output - so I prefer
> QString::arg() to QString::sprintf(). The use of precision==-1 is not
> documented - at least not in qt 4.6 api-doc.
>
> Thank in advance,
>
> Charly
>
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