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Subject: |
Documentation of format doesn't describe "g" accurately |
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Date: |
Fri, 27 Jan 2017 17:05:28 -0500 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 |
Hi emacs,
There seems to be a few issues in the docstring of `format':
> %g means print a number in exponential notation
> or decimal-point notation, whichever uses fewer characters.
This seems wrong:
(format "%g" 3.0) ⇒ "3", but
(format "%f" 3.0) ⇒ "3.000000", and
(format "%e" 3.0) ⇒ "3.000000e+00", so %g is neither %f nor %e.
> The # flag means to use an alternate display form [...]
> for %e, %f, and %g, it causes a decimal point to be included even if
> the precision is zero.
This seems incomplete:
(format "%#.5g" 3) ⇒ "3.0000", while
(format "%.5g" 3) ⇒ "3", so # doesn't just cause changes when the precision
is 0.
> For %e, %f, and %g sequences, the number after the "." in the
> precision specifier says how many decimal places to show
This seems wrong, too:
(format "%.5g" 3.0) ⇒ "3", not "3.00000"
(format "%.5g" 3.1) ⇒ "3.1", not "3.10000"
Similar problems seem to exist in the actual documentation. On a related note,
is there a way to get a shortest representation of a number? Something like %g,
but without exponents.
Thanks!
Clément.
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--- Begin Message ---
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Subject: |
Re: bug#25557: Documentation of format doesn't describe "g" accurately |
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Date: |
Sat, 28 Jan 2017 10:37:25 +0200 |
> From: Clément Pit--Claudel <address@hidden>
> Date: Fri, 27 Jan 2017 17:05:28 -0500
>
> There seems to be a few issues in the docstring of `format':
>
> > %g means print a number in exponential notation
> > or decimal-point notation, whichever uses fewer characters.
>
> This seems wrong:
>
> (format "%g" 3.0) ⇒ "3", but
> (format "%f" 3.0) ⇒ "3.000000", and
> (format "%e" 3.0) ⇒ "3.000000e+00", so %g is neither %f nor %e.
Fixed.
> > The # flag means to use an alternate display form [...]
> > for %e, %f, and %g, it causes a decimal point to be included even if
> > the precision is zero.
>
> This seems incomplete:
>
> (format "%#.5g" 3) ⇒ "3.0000", while
> (format "%.5g" 3) ⇒ "3", so # doesn't just cause changes when the precision
> is 0.
I don't understand what you are trying to say (nor the significance of
the '.' flag in the example). '#' forces %g to leave the trailing
zeros after the decimal, so I added that -- is that what you wanted to
say?
> > For %e, %f, and %g sequences, the number after the "." in the
> > precision specifier says how many decimal places to show
>
> This seems wrong, too:
>
> (format "%.5g" 3.0) ⇒ "3", not "3.00000"
> (format "%.5g" 3.1) ⇒ "3.1", not "3.10000"
Fixed.
> Similar problems seem to exist in the actual documentation.
If you mean the ELisp manual, I fixed that as well.
> On a related note, is there a way to get a shortest representation of a
> number? Something like %g, but without exponents.
Sorry, I don't understand the question. How can you represent an
arbitrary number without exponents at all, except by %f?
Anyway, thanks; I'm marking this bug done.
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