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fmt: width is measured in bytes not Unicode codepoints when using %c and %q for runes #8275

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gopherbot opened this issue Jun 23, 2014 · 5 comments
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@gopherbot
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@gopherbot gopherbot commented Jun 23, 2014

by MihaiBorobocea:

What does 'go version' print?
go1.3

What steps reproduce the problem?
package main

import "fmt"

func main() {
    fmt.Printf("(%5q)\n", "§") // (  "§")
    fmt.Printf("(%5q)\n", '§')   // ( '§')

    fmt.Printf("(%3s)\n", "§") // (  §)
    fmt.Printf("(%3c)\n", '§')   // ( §)
}

// Or run this same program at http://play.golang.org/p/UHE8wQK50u

What happened?
When printing a rune with %q or %c and specifying a width (for padding with spaces) the
width is counted in bytes. The program prints the rune U+00A7 which uses 2 bytes in
UTF-8. The lines with rune args produce a string shorter than the corresponding lines
with string args.

What should have happened instead?
The width should have been measured in runes, like it happens when printing a string.
Package fmt's doc says “Width and precision are measured in units of Unicode code
points”.

Am I misunderstanding how this is supposed to work? This seems too basic to have gone
unnoticed.
I've tried to find this in the code, and I'll attach an RFC diff in case my progress
saves you some time.
@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Jun 23, 2014

Comment 1:

Labels changed: added repo-main, release-go1.4.

@gopherbot
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@gopherbot gopherbot commented Jun 24, 2014

Comment 2 by MihaiBorobocea:

I've submitted my progress at https://golang.org/cl/104320043
@robpike
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@robpike robpike commented Jul 29, 2014

Comment 3:

Status changed to Accepted.

@gopherbot
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@gopherbot gopherbot commented Jul 29, 2014

Comment 4:

CL https://golang.org/cl/104320043 mentions this issue.
@robpike
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@robpike robpike commented Jul 29, 2014

Comment 5:

This issue was closed by revision bfdeb57.

Status changed to Fixed.

@rsc rsc added this to the Go1.4 milestone Apr 14, 2015
@rsc rsc removed the release-go1.4 label Apr 14, 2015
@golang golang locked and limited conversation to collaborators Jun 25, 2016
wheatman added a commit to wheatman/go-akaros that referenced this issue Jun 25, 2018
This is meant to share my progress on Issue 8275, if it's useful to you. I'm not familiar with the formatter's internals, so this change is likely naive.

Change these calls to measure width in runes not bytes:
fmt.Printf("(%5q)\n", '§')
fmt.Printf("(%3c)\n", '§')

 Fixes golang#8275.

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/104320043
wheatman added a commit to wheatman/go-akaros that referenced this issue Jul 9, 2018
This is meant to share my progress on Issue 8275, if it's useful to you. I'm not familiar with the formatter's internals, so this change is likely naive.

Change these calls to measure width in runes not bytes:
fmt.Printf("(%5q)\n", '§')
fmt.Printf("(%3c)\n", '§')

 Fixes golang#8275.

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/104320043
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