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fmt: float64 formatting behaving differently than expected (and than documented) #18772

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vvekic opened this issue Jan 24, 2017 · 5 comments
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fmt: float64 formatting behaving differently than expected (and than documented) #18772

vvekic opened this issue Jan 24, 2017 · 5 comments
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Documentation Issues describing a change to documentation. FrozenDueToAge
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Go1.9

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@vvekic
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vvekic commented Jan 24, 2017 •
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What version of Go are you using (go version)?

1.7.3

What operating system and processor architecture are you using (go env)?

darwin amd64

What did you do?

https://play.golang.org/p/LEVTU7r4wX

What did you expect to see?

The %g-formatted (or %v) float64 number to be the same as either %f or %e, as per documentation.

What did you see instead?

The %g-formatted number was 24.849999999999998.
@ianlancetaylor ianlancetaylor changed the title float64 formatting behaving differently than expected (and than documented) fmt: float64 formatting behaving differently than expected (and than documented) Jan 24, 2017
@ianlancetaylor ianlancetaylor added this to the Go1.9 milestone Jan 24, 2017
@ALTree
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ALTree commented Jan 24, 2017

The default precision for %e and %f is 6; for %g it is the smallest number of digits necessary to identify the value uniquely.

@ianlancetaylor
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Probably needs a doc tweak, as the short description of %g does suggest that it is either %e or %f.

CC @robpike @martisch

@ianlancetaylor ianlancetaylor added the Documentation Issues describing a change to documentation. label Jan 24, 2017
@rsc
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rsc commented Jan 24, 2017

There's only so much we can say in a one-line summary. The full details of the precision are documented. I tend to think this is fine as is, unless someone can come up with a very short replacement for the current one-line summary.

@griesemer
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It may suffice to replace

%g	%e for large exponents, %f otherwise

with

%g	%e for large exponents, %f otherwise (see below for default precision in this case)

@robpike robpike self-assigned this Jan 24, 2017
@ThibaultRiviere ThibaultRiviere mentioned this issue Jan 26, 2017
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@gopherbot
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CL https://golang.org/cl/37313 mentions this issue.

@golang golang locked and limited conversation to collaborators Feb 21, 2018
@rsc rsc unassigned robpike Jun 23, 2022
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@rsc @ianlancetaylor @ALTree @robpike @vvekic @griesemer @gopherbot