fmt: %q with byte value

[3052]

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]

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"
}

[Goclipse27]

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))

}