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List:       kde-devel
Subject:    Re: dump question
From:       Christian Esken <c.esken () cityweb ! de>
Date:       1999-08-08 17:09:40
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On Sun, 08 Aug 1999 Uwe Thiem wrote:
>I'm stuck with a little problem I'm too dump to solve it seems. Maybe
>someone else can shed some light on it.
>
>This is the code:
>
>double tmp = mRealCenter - mRealWidth / 2.0;
>
>QString s;
>s.setNum( tmp, 'f', 60 );
>cerr << s << "\n";
>for ( i = 0, p = mReals; i < 3; i++, p++ )
>  {
>  s.setNum( (double) i * mRealWidth / (double) mWidth, 'f', 60 );
>  cerr << s << "\n";
>  s.setNum( tmp + (double) i * mRealWidth / (double) mWidth, 'f', 60 );

I would bet the problem is in above line: Doing setNum() converts.
An implicit cast will happen to "tmp". It might be converted to "anything"
appropiate, for example to int or float. float could be a too small data type.

Solution: Always store the data in appropiate datas types.
IMO storing a float (double) in a string and then resuing it to do
calculations is a very dangerous way of handling data, IMO.

I didnīt test the following code, but I think it works out OK.

double d_tmp;
d_tmp = double(tmp)
for ( i = 0, p = mReals; i < 3; i++, p++ )
  {
  QString s;
  double a,b;
  a = (double) i * mRealWidth / (double) mWidth;
  cerr << a << "\n";
  b = d_tmp + a;
  cerr << b << "\n";
  s.setNum( b, 'f', 60 );
  cerr << s << "\n";
  }
cerr << "\n";


  Christian

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