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fmt: %q with byte value #63646

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3052 opened this issue Oct 20, 2023 · 2 comments
Closed

fmt: %q with byte value #63646

3052 opened this issue Oct 20, 2023 · 2 comments
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Documentation NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.

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@3052
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3052 commented Oct 20, 2023 •
edited

If I run this code:

package main

import "fmt"

func main() {
   fmt.Printf("%s\n", "\xA1") 
   fmt.Printf("%q\n", "\xA1") 
   fmt.Printf("%c\n", rune(0xA1)) 
   fmt.Printf("%q\n", rune(0xA1)) 
   fmt.Printf("%c\n", byte(0xA1)) 
   fmt.Printf("%q\n", byte(0xA1)) 
}

I get this result:

�
"\xa1"
¡
'¡'
¡
'¡'

everything seems OK except for the last two items. INVERTED EXCLAMATION MARK (U+00A1) is actually 0xC2 0xA1 in UTF-8, not just 0xA1. with %c, this is explained in the documentation:

go/src/fmt/doc.go

Lines 26 to 33 in 693def1

Integer:
%b base 2
%c the character represented by the corresponding Unicode code point
%d base 10
%o base 8
%O base 8 with 0o prefix
%q a single-quoted character literal safely escaped with Go syntax.

but %q doesn't seem to be clear enough about what its doing. it seems with both %c and %q, a byte value is first converted to a rune before printing, but only %c draws attention to that fact. I think the current behavior is correct, but the %q value documentation should be more explicit about the conversion to a rune/Unicode code point.
@3052
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3052 commented Oct 20, 2023

looks like this is related to 5 here:

https://go.dev/ref/spec#Conversions_to_and_from_a_string_type

as a workaround, you can use a byte slice instead:

package main

import "fmt"

func main() {
   fmt.Printf("%s\n", []byte{0xA1}) // �
   fmt.Printf("%q\n", []byte{0xA1}) // "\xa1"
}

@seankhliao seankhliao added Documentation NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Oct 21, 2023
@raghvenders
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raghvenders commented Oct 26, 2023 •
edited

Inverted exclamation is within a byte and hope the below helps


package main

import "fmt"

func main() {
	fmt.Printf("%s\n", "\xC2\xA1")
	fmt.Printf("%q\n", "\xC2\xA1")
	fmt.Printf("%+q\n", "\xC2\xA1")
	fmt.Printf("%#U\n", rune(0xA1))

}

@3052 3052 closed this as completed Oct 29, 2023
@3052 3052 reopened this Oct 29, 2023
@3052 3052 closed this as completed Nov 26, 2023
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