Re: Convert float to double - weird failure

tugboat90 wrote:

I am trying to cast a float to a double (in C++) and am using the
static cast functionality. However, the value returned from the
static cast is not correct.

Example:
// Define a float
float f = 1.20000;

// Cast into a double - after the cast, the value of "d" is
// is "1.20000498297"
double d = static_cast<double> (f);

Is there some reason why the last few places are filled with garbage
now? I would have thought it would have been filled with 0's.

Yes. floats (and doubles) are based on binary representations, and
in your system they cannot exactly represent the value of 1.2.
Thus the value of f is set to the closest float approximation to
1.2 available. Now d is set to that value (not 1.2) whatever it
is.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>



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