# package utf8 `import "unicode/utf8"` utf8包實現了對utf-8文本的常用函數和常數的支持，包括rune和utf-8編碼byte序列之間互相翻譯的函數。 ## Index * [Constants](#pkg-constants) * [func ValidRune(r rune) bool](#ValidRune) * [func RuneLen(r rune) int](#RuneLen) * [func RuneStart(b byte) bool](#RuneStart) * [func FullRune(p []byte) bool](#FullRune) * [func FullRuneInString(s string) bool](#FullRuneInString) * [func Valid(p []byte) bool](#Valid) * [func ValidString(s string) bool](#ValidString) * [func RuneCount(p []byte) int](#RuneCount) * [func RuneCountInString(s string) int](#RuneCountInString) * [func EncodeRune(p []byte, r rune) int](#EncodeRune) * [func DecodeRune(p []byte) (r rune, size int)](#DecodeRune) * [func DecodeRuneInString(s string) (r rune, size int)](#DecodeRuneInString) * [func DecodeLastRune(p []byte) (r rune, size int)](#DecodeLastRune) * [func DecodeLastRuneInString(s string) (r rune, size int)](#DecodeLastRuneInString) ### Examples * [DecodeLastRune](#example-DecodeLastRune) * [DecodeLastRuneInString](#example-DecodeLastRuneInString) * [DecodeRune](#example-DecodeRune) * [DecodeRuneInString](#example-DecodeRuneInString) * [EncodeRune](#example-EncodeRune) * [FullRune](#example-FullRune) * [FullRuneInString](#example-FullRuneInString) * [RuneCount](#example-RuneCount) * [RuneCountInString](#example-RuneCountInString) * [RuneLen](#example-RuneLen) * [RuneStart](#example-RuneStart) * [Valid](#example-Valid) * [ValidRune](#example-ValidRune) * [ValidString](#example-ValidString) ## Constants ``` const ( RuneError = '\uFFFD' // 錯誤的Rune或"Unicode replacement character" RuneSelf = 0x80 // 低于RunSelf的字符用代表單字節的同一值表示 MaxRune = '\U0010FFFF' // 最大的合法unicode碼值 UTFMax = 4 // 最大的utf-8編碼的unicode字符的長度 ) ``` 編碼的基礎常數。 ## func [ValidRune](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L425 "View Source") ``` func ValidRune(r rune) bool ``` 判斷r是否可以編碼為合法的utf-8序列。 Example ``` valid := 'a' invalid := rune(0xfffffff) fmt.Println(utf8.ValidRune(valid)) fmt.Println(utf8.ValidRune(invalid)) ``` Output: ``` true false ``` ## func [RuneLen](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L310 "View Source") ``` func RuneLen(r rune) int ``` 返回r編碼后的字節數。如果r不是一個合法的可編碼為utf-8序列的值，會返回-1。 Example ``` fmt.Println(utf8.RuneLen('a')) fmt.Println(utf8.RuneLen('界')) ``` Output: ``` 1 3 ``` ## func [RuneStart](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L384 "View Source") ``` func RuneStart(b byte) bool ``` 報告字節b是否可以作為某個rune編碼后的第一個字節。第二個即之后的字節總是將左端兩個字位設為10。 Example ``` buf := []byte("a界") fmt.Println(utf8.RuneStart(buf[0])) fmt.Println(utf8.RuneStart(buf[1])) fmt.Println(utf8.RuneStart(buf[2])) ``` Output: ``` true true false ``` ## func [FullRune](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L203 "View Source") ``` func FullRune(p []byte) bool ``` 報告切片p是否以一個碼值的完整utf-8編碼開始。不合法的編碼因為會被轉換為寬度1的錯誤碼值而被視為完整的。 Example ``` buf := []byte{228, 184, 150} // 世 fmt.Println(utf8.FullRune(buf)) fmt.Println(utf8.FullRune(buf[:2])) ``` Output: ``` true false ``` ## func [FullRuneInString](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L209 "View Source") ``` func FullRuneInString(s string) bool ``` 函數類似FullRune但輸入參數是字符串。 Example ``` str := "世" fmt.Println(utf8.FullRuneInString(str)) fmt.Println(utf8.FullRuneInString(str[:2])) ``` Output: ``` true false ``` ## func [RuneCount](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L359 "View Source") ``` func RuneCount(p []byte) int ``` 返回p中的utf-8編碼的碼值的個數。錯誤或者不完整的編碼會被視為寬度1字節的單個碼值。 Example ``` buf := []byte("Hello, 世界") fmt.Println("bytes =", len(buf)) fmt.Println("runes =", utf8.RuneCount(buf)) ``` Output: ``` bytes = 13 runes = 9 ``` ## func [RuneCountInString](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L374 "View Source") ``` func RuneCountInString(s string) (n int) ``` 函數類似RuneCount但輸入參數是一個字符串。 Example ``` str := "Hello, 世界" fmt.Println("bytes =", len(str)) fmt.Println("runes =", utf8.RuneCountInString(str)) ``` Output: ``` bytes = 13 runes = 9 ``` ## func [Valid](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L387 "View Source") ``` func Valid(p []byte) bool ``` 返回切片p是否包含完整且合法的utf-8編碼序列。 Example ``` valid := []byte("Hello, 世界") invalid := []byte{0xff, 0xfe, 0xfd} fmt.Println(utf8.Valid(valid)) fmt.Println(utf8.Valid(invalid)) ``` Output: ``` true false ``` ## func [ValidString](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L407 "View Source") ``` func ValidString(s string) bool ``` 報告s是否包含完整且合法的utf-8編碼序列。 Example ``` valid := "Hello, 世界" invalid := string([]byte{0xff, 0xfe, 0xfd}) fmt.Println(utf8.ValidString(valid)) fmt.Println(utf8.ValidString(invalid)) ``` Output: ``` true false ``` ## func [EncodeRune](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L330 "View Source") ``` func EncodeRune(p []byte, r rune) int ``` EncodeRune將r的utf-8編碼序列寫入p（p必須有足夠的長度），并返回寫入的字節數。 Example ``` r := '世' buf := make([]byte, 3) n := utf8.EncodeRune(buf, r) fmt.Println(buf) fmt.Println(n) ``` Output: ``` [228 184 150] 3 ``` ## func [DecodeRune](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L219 "View Source") ``` func DecodeRune(p []byte) (r rune, size int) ``` 函數解碼p開始位置的第一個utf-8編碼的碼值，返回該碼值和編碼的字節數。如果編碼不合法，會返回(RuneError, 1)。該返回值在正確的utf-8編碼情況下是不可能返回的。 如果一個utf-8編碼序列格式不正確，或者編碼的碼值超出utf-8合法碼值的范圍，或者不是該碼值的最短編碼，該編碼序列即是不合法的。函數不會執行其他的驗證。 Example ``` b := []byte("Hello, 世界") for len(b) > 0 { r, size := utf8.DecodeRune(b) fmt.Printf("%c %v\n", r, size) b = b[size:] } ``` Output: ``` H 1 e 1 l 1 l 1 o 1 , 1 1 世 3 界 3 ``` ## func [DecodeRuneInString](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L229 "View Source") ``` func DecodeRuneInString(s string) (r rune, size int) ``` 函數類似DecodeRune但輸入參數是字符串。 Example ``` str := "Hello, 世界" for len(str) > 0 { r, size := utf8.DecodeRuneInString(str) fmt.Printf("%c %v\n", r, size) str = str[size:] } ``` Output: ``` H 1 e 1 l 1 l 1 o 1 , 1 1 世 3 界 3 ``` ## func [DecodeLastRune](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L239 "View Source") ``` func DecodeLastRune(p []byte) (r rune, size int) ``` 函數解碼p中最后一個utf-8編碼序列，返回該碼值和編碼序列的長度。 Example ``` 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] } ``` Output: ``` 界 3 世 3 1 , 1 o 1 l 1 l 1 e 1 H 1 ``` ## func [DecodeLastRuneInString](https://github.com/golang/go/blob/master/src/unicode/utf8/utf8.go#L276 "View Source") ``` func DecodeLastRuneInString(s string) (r rune, size int) ``` 函數類似DecodeLastRune但輸入參數是字符串。 Example ``` 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] } ``` Output: ``` 界 3 世 3 1 , 1 o 1 l 1 l 1 e 1 H 1 ```