How to detect a double's significant digits

[Fredrik Lundh]

Jeremy Bowers wrote:

> > A step which will require him to tell the printing routine how many digits
> > he wants printed.
>
> Not necessarily; consider the str() of a float in Python, especially given
> the "significant digits" aspect (it may be ill-defined, but I can think of
> several well-defined ways to mean that, where str() embodies one of them).
> The easiest way to tell how long the number will be when str prints it out
> is to simply ask it.

and what language is str() implemented in?

> In C++, this may be harder, as your output software may insist on
> rendering everything directly, with no way to reach in and tell what it
> did. Imagine the standard IOStreams, without the ability to stream into a
> string.

but you can stream into a string buffer, and you can use sprintf() from C++,
so what's your point, besides stating that "if things were harder, they would
be harder"?

</F>