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Package utf8

import "unicode/utf8"
Overview
Index
Examples

Overview ▾

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.

Constants

Numbers fundamental to the encoding.

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.
)

func DecodeLastRune

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, non-empty 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.

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

Example

界 3
世 3
  1
, 1
o 1
l 1
l 1
e 1
H 1

func DecodeLastRuneInString

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, non-empty 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.

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

Example

界 3
世 3
  1
, 1
o 1
l 1
l 1
e 1
H 1

func DecodeRune

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, non-empty 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.

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

Example

H 1
e 1
l 1
l 1
o 1
, 1
  1
世 3
界 3

func DecodeRuneInString

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, non-empty 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.

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

Example

H 1
e 1
l 1
l 1
o 1
, 1
  1
世 3
界 3

func EncodeRune

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

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

Example

[228 184 150]
3

func FullRune

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.

func FullRune(p []byte) bool

Example

true
false

func FullRuneInString

FullRuneInString is like FullRune but its input is a string.

func FullRuneInString(s string) bool

Example

true
false

func RuneCount

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

func RuneCount(p []byte) int

Example

bytes = 13
runes = 9

func RuneCountInString

RuneCountInString is like RuneCount but its input is a string.

func RuneCountInString(s string) (n int)

Example

bytes = 13
runes = 9

func RuneLen

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.

func RuneLen(r rune) int

Example

1
3

func RuneStart

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

func RuneStart(b byte) bool

Example

true
true
false

func Valid

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

func Valid(p []byte) bool

Example

true
false

func ValidRune

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

func ValidRune(r rune) bool

Example

true
false

func ValidString

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

func ValidString(s string) bool

Example

true
false