package utf8

import "unicode/utf8"

Package utf8 implements functions and constants to support text encoded in UTF-8. It includes functions to translate between runes and UTF-8 byte sequences.

Index ¶

• Constants
• func DecodeLastRune(p []byte) (r rune, size int)
• func DecodeLastRuneInString(s string) (r rune, size int)
• func DecodeRune(p []byte) (r rune, size int)
• func DecodeRuneInString(s string) (r rune, size int)
• func EncodeRune(p []byte, r rune) int
• func FullRune(p []byte) bool
• func FullRuneInString(s string) bool
• func RuneCount(p []byte) int
• func RuneCountInString(s string) (n int)
• func RuneLen(r rune) int
• func RuneStart(b byte) bool
• func Valid(p []byte) bool
• func ValidRune(r rune) bool
• func ValidString(s string) bool

Examples ¶

• DecodeLastRune
• DecodeLastRuneInString
• DecodeRune
• DecodeRuneInString
• EncodeRune
• FullRune
• FullRuneInString
• RuneCount
• RuneCountInString
• RuneLen
• RuneStart
• Valid
• ValidRune
• ValidString

Constants ¶

const (
	RuneError = '\uFFFD'     // the "error" Rune or "Unicode replacement character"
	RuneSelf  = 0x80         // characters below Runeself are represented as themselves in a single byte.
	MaxRune   = '\U0010FFFF' // Maximum valid Unicode code point.
	UTFMax    = 4            // maximum number of bytes of a UTF-8 encoded Unicode character.
)

Numbers fundamental to the encoding.

Functions ¶

func DecodeLastRune ¶

func DecodeLastRune(p []byte) (r rune, size int)

DecodeLastRune unpacks the last UTF-8 encoding in p and returns the rune and its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if the encoding is invalid, it returns (RuneError, 1). Both are impossible results for correct UTF-8.

An encoding is invalid if it is incorrect UTF-8, encodes a rune that is out of range, or is not the shortest possible UTF-8 encoding for the value. No other validation is performed.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	b := []byte("Hello, 世界")

	for len(b) > 0 {
		r, size := utf8.DecodeLastRune(b)
		fmt.Printf("%c %v\n", r, size)

		b = b[:len(b)-size]
	}
}

界 3
世 3
  1
, 1
o 1
l 1
l 1
e 1
H 1

func DecodeLastRuneInString ¶

func DecodeLastRuneInString(s string) (r rune, size int)

DecodeLastRuneInString is like DecodeLastRune but its input is a string. If s is empty it returns (RuneError, 0). Otherwise, if the encoding is invalid, it returns (RuneError, 1). Both are impossible results for correct UTF-8.

An encoding is invalid if it is incorrect UTF-8, encodes a rune that is out of range, or is not the shortest possible UTF-8 encoding for the value. No other validation is performed.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	str := "Hello, 世界"

	for len(str) > 0 {
		r, size := utf8.DecodeLastRuneInString(str)
		fmt.Printf("%c %v\n", r, size)

		str = str[:len(str)-size]
	}
}

界 3
世 3
  1
, 1
o 1
l 1
l 1
e 1
H 1

func DecodeRune ¶

func DecodeRune(p []byte) (r rune, size int)

DecodeRune unpacks the first UTF-8 encoding in p and returns the rune and its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if the encoding is invalid, it returns (RuneError, 1). Both are impossible results for correct UTF-8.

An encoding is invalid if it is incorrect UTF-8, encodes a rune that is out of range, or is not the shortest possible UTF-8 encoding for the value. No other validation is performed.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	b := []byte("Hello, 世界")

	for len(b) > 0 {
		r, size := utf8.DecodeRune(b)
		fmt.Printf("%c %v\n", r, size)

		b = b[size:]
	}
}

H 1
e 1
l 1
l 1
o 1
, 1
  1
世 3
界 3

func DecodeRuneInString ¶

func DecodeRuneInString(s string) (r rune, size int)

DecodeRuneInString is like DecodeRune but its input is a string. If s is empty it returns (RuneError, 0). Otherwise, if the encoding is invalid, it returns (RuneError, 1). Both are impossible results for correct UTF-8.

An encoding is invalid if it is incorrect UTF-8, encodes a rune that is out of range, or is not the shortest possible UTF-8 encoding for the value. No other validation is performed.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	str := "Hello, 世界"

	for len(str) > 0 {
		r, size := utf8.DecodeRuneInString(str)
		fmt.Printf("%c %v\n", r, size)

		str = str[size:]
	}
}

H 1
e 1
l 1
l 1
o 1
, 1
  1
世 3
界 3

func EncodeRune ¶

func EncodeRune(p []byte, r rune) int

EncodeRune writes into p (which must be large enough) the UTF-8 encoding of the rune. It returns the number of bytes written.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	r := '世'
	buf := make([]byte, 3)

	n := utf8.EncodeRune(buf, r)

	fmt.Println(buf)
	fmt.Println(n)
}

[228 184 150]
3

func FullRune ¶

func FullRune(p []byte) bool

FullRune reports whether the bytes in p begin with a full UTF-8 encoding of a rune. An invalid encoding is considered a full Rune since it will convert as a width-1 error rune.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	buf := []byte{228, 184, 150} // 世
	fmt.Println(utf8.FullRune(buf))
	fmt.Println(utf8.FullRune(buf[:2]))
}

true
false

func FullRuneInString ¶

func FullRuneInString(s string) bool

FullRuneInString is like FullRune but its input is a string.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	str := "世"
	fmt.Println(utf8.FullRuneInString(str))
	fmt.Println(utf8.FullRuneInString(str[:2]))
}

true
false

func RuneCount ¶

func RuneCount(p []byte) int

RuneCount returns the number of runes in p. Erroneous and short encodings are treated as single runes of width 1 byte.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	buf := []byte("Hello, 世界")
	fmt.Println("bytes =", len(buf))
	fmt.Println("runes =", utf8.RuneCount(buf))
}

bytes = 13
runes = 9

func RuneCountInString ¶

func RuneCountInString(s string) (n int)

RuneCountInString is like RuneCount but its input is a string.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	str := "Hello, 世界"
	fmt.Println("bytes =", len(str))
	fmt.Println("runes =", utf8.RuneCountInString(str))
}

bytes = 13
runes = 9

func RuneLen ¶

func RuneLen(r rune) int

RuneLen returns the number of bytes required to encode the rune. It returns -1 if the rune is not a valid value to encode in UTF-8.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	fmt.Println(utf8.RuneLen('a'))
	fmt.Println(utf8.RuneLen('界'))
}

1
3

func RuneStart ¶

func RuneStart(b byte) bool

RuneStart reports whether the byte could be the first byte of an encoded rune. Second and subsequent bytes always have the top two bits set to 10.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	buf := []byte("a界")
	fmt.Println(utf8.RuneStart(buf[0]))
	fmt.Println(utf8.RuneStart(buf[1]))
	fmt.Println(utf8.RuneStart(buf[2]))
}

true
true
false

func Valid ¶

func Valid(p []byte) bool

Valid reports whether p consists entirely of valid UTF-8-encoded runes.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	valid := []byte("Hello, 世界")
	invalid := []byte{0xff, 0xfe, 0xfd}

	fmt.Println(utf8.Valid(valid))
	fmt.Println(utf8.Valid(invalid))
}

true
false

func ValidRune ¶

func ValidRune(r rune) bool

ValidRune reports whether r can be legally encoded as UTF-8. Code points that are out of range or a surrogate half are illegal.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	valid := 'a'
	invalid := rune(0xfffffff)

	fmt.Println(utf8.ValidRune(valid))
	fmt.Println(utf8.ValidRune(invalid))
}

true
false

func ValidString ¶

func ValidString(s string) bool

ValidString reports whether s consists entirely of valid UTF-8-encoded runes.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	valid := "Hello, 世界"
	invalid := string([]byte{0xff, 0xfe, 0xfd})

	fmt.Println(utf8.ValidString(valid))
	fmt.Println(utf8.ValidString(invalid))
}

true
false

Source Files ¶

utf8.go