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fmt: %#g behavior not consistent #36562

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musiphil opened this issue Jan 15, 2020 · 3 comments
Closed

fmt: %#g behavior not consistent #36562

musiphil opened this issue Jan 15, 2020 · 3 comments
Labels
FrozenDueToAge help wanted NeedsFix The path to resolution is known, but the work has not been done.
Milestone
Go1.15

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@musiphil
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What version of Go are you using (go version)?

$ go version
go version go1.13.4 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="$HOME/.cache/go-build"
GOENV="$HOME/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="$HOME/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/google-golang"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/google-golang/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build990462557=/tmp/go-build -gno-record-gcc-switches"

What did you do?

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

fmt.Printf("%#.4g\n", 1.234)
fmt.Printf("%#.4g\n", 0.1234)
fmt.Printf("%#.4g\n", 1.23)
fmt.Printf("%#.4g\n", 0.123)
fmt.Printf("%#.4g\n", 1.2)
fmt.Printf("%#.4g\n", 0.12)

What did you expect to see?

1.234
0.1234
1.230
0.1230
1.200
0.1200

%#.4g should print 4 significant digits, without removing trailing zeros.

What did you see instead?

1.234
0.1234
1.230
0.123
1.200
0.120

The trailing zero from 1.230 is erroneously removed.
@martisch
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Contributor

martisch commented Jan 15, 2020 •
edited

This seems consistent with the documentation (https://godoc.org/fmt) of the g verb and precision:

"For floating-point values, width sets the minimum width of the field and precision sets the number of places after the decimal, if appropriate, except that for %g/%G precision sets the maximum number of significant digits (trailing zeros are removed)."

@martisch martisch added the WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. label Jan 15, 2020
@martisch
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martisch commented Jan 15, 2020 •
edited

I see now that # is supposed to alter the g verb behavior to not remove trailing zeros later in the documentation.

"do not remove trailing zeros for %g and %G;"

So you are right this should have trailing zeros.

@martisch martisch removed the WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. label Jan 15, 2020
@martisch martisch added this to the Go1.15 milestone Jan 15, 2020
@martisch martisch self-assigned this Jan 15, 2020
@martisch martisch added NeedsFix The path to resolution is known, but the work has not been done. help wanted labels Jan 15, 2020
yah01 added a commit to yah01/go that referenced this issue Jan 15, 2020
@yah01
fixes golang#36562
ca6628b
@yah01 yah01 mentioned this issue Jan 15, 2020
Closed
@gopherbot
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Change https://golang.org/cl/215001 mentions this issue: fmt: do not remove trailing zeros for %g and %G with #(sharp) flag

yah01 added a commit to yah01/go that referenced this issue Jan 16, 2020
@yah01
fix golang#36562
586da2c
yah01 added a commit to yah01/go that referenced this issue Jan 18, 2020
@yah01
fix golang#36562
6768429
yah01 added a commit to yah01/go that referenced this issue Jan 18, 2020
@yah01
fixes golang#36562
6e1f2b6
@martisch martisch removed their assignment Jan 18, 2020
@golang golang locked and limited conversation to collaborators Feb 25, 2021
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fmt: do not remove trailing zeros for %g and %G with #(sharp) flag yah01/go
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@martisch @musiphil @gopherbot