Golang之bytes.buffer · Golang學習室

> bytes.buffer是一個緩沖byte類型的緩沖器存放著都是byte Buffer 是 bytes 包中的一個 type Buffer struct{…} > A buffer is a variable-sized buffer of bytes with Read and Write methods. The zero value for Buffer is an empty buffer ready to use. （是一個變長的 buffer，具有 Read 和Write 方法。 Buffer 的零值是一個空的 buffer，但是可以使用） Buffer 就像一個集裝箱容器，可以存東西，取東西（存取數據） - 創建一個 Buffer （其實底層就是一個 []byte，字節切片） - 向其中寫入數據 (Write mtheods) - 從其中讀取數據 (Write methods) # 創建 Buffer緩沖器 ~~~ var b bytes.Buffer //直接定義一個 Buffer 變量，而不用初始化 b.Writer([]byte("Hello ")) // 可以直接使用 b1 := new(bytes.Buffer) //直接使用 new 初始化，可以直接使用 // 其它兩種定義方式 func NewBuffer(buf []byte) *Buffer func NewBufferString(s string) *Buffer ~~~ ### NewBuffer ~~~ // NewBuffer creates and initializes a new Buffer using buf as its initial // contents. It is intended to prepare a Buffer to read existing data. It // can also be used to size the internal buffer for writing. To do that, // buf should have the desired capacity but a length of zero. // // In most cases, new(Buffer) (or just declaring a Buffer variable) is // sufficient to initialize a Buffer. func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} } ~~~ - NewBuffer使用buf作為參數初始化Buffer， - Buffer既可以被讀也可以被寫 - 如果是讀Buffer，buf需填充一定的數據 - 如果是寫，buf需有一定的容量(capacity)，當然也可以通過new(Buffer)來初始化Buffer。另外一個方法NewBufferString用一個string來初始化可讀Buffer，并用string的內容填充Buffer. ~~~ func IntToBytes(n int) []byte { x := int32(n) //創建一個內容是[]byte的slice的緩沖器 //與bytes.NewBufferString("")等效 bytesBuffer := bytes.NewBuffer([]byte{}) binary.Write(bytesBuffer, binary.BigEndian, x) return bytesBuffer.Bytes() } ~~~ ### NewBufferString - 方法NewBufferString用一個string來初始化可讀Buffer，并用string的內容填充Buffer. - 用法和NewBuffer沒有太大區別 ~~~ // NewBufferString creates and initializes a new Buffer using string s as its // initial contents. It is intended to prepare a buffer to read an existing // string. // // In most cases, new(Buffer) (or just declaring a Buffer variable) is // sufficient to initialize a Buffer. func NewBufferString(s string) *Buffer { return &Buffer{buf: []byte(s)} } ~~~ ~~~ func TestBufferString(){ buf1:=bytes.NewBufferString("swift") buf2:=bytes.NewBuffer([]byte("swift")) buf3:=bytes.NewBuffer([]byte{'s','w','i','f','t'}) fmt.Println("===========以下buf1,buf2,buf3等效=========") fmt.Println("buf1:", buf1) fmt.Println("buf2:", buf2) fmt.Println("buf3:", buf3) fmt.Println("===========以下創建空的緩沖器等效=========") buf4:=bytes.NewBufferString("") buf5:=bytes.NewBuffer([]byte{}) fmt.Println("buf4:", buf4) fmt.Println("buf5:", buf5) } ~~~ 輸出： > ===========以下buf1,buf2,buf3等效========= buf1: swift buf2: swift buf3: swift ===========以下創建空的緩沖器等效========= buf4: buf5: # 向 Buffer 中寫入數據 ### Write 把字節切片 p 寫入到buffer中去。 ~~~ // Write appends the contents of p to the buffer, growing the buffer as // needed. The return value n is the length of p; err is always nil. If the // buffer becomes too large, Write will panic with ErrTooLarge. func (b *Buffer) Write(p []byte) (n int, err error) { b.lastRead = opInvalid m := b.grow(len(p)) return copy(b.buf[m:], p), nil } ~~~ ~~~ fmt.Println("===========以下通過Write把swift寫入Learning緩沖器尾部=========") newBytes := []byte("swift") //創建一個內容Learning的緩沖器 buf := bytes.NewBuffer([]byte("Learning")) //打印為Learning fmt.Println(buf.String()) //將newBytes這個slice寫到buf的尾部 buf.Write(newBytes) fmt.Println(buf.String()) ~~~ 打印： > ===========以下通過Write把swift寫入Learning緩沖器尾部========= Learning Learningswift ### WriteString 使用WriteString方法，將一個字符串放到緩沖器的尾部 ~~~ // WriteString appends the contents of s to the buffer, growing the buffer as // needed. The return value n is the length of s; err is always nil. If the // buffer becomes too large, WriteString will panic with ErrTooLarge. func (b *Buffer) WriteString(s string) (n int, err error) { b.lastRead = opInvalid m := b.grow(len(s)) return copy(b.buf[m:], s), nil } ~~~ ~~~ fmt.Println("===========以下通過WriteString把swift寫入Learning緩沖器尾部=========") newString := "swift" //創建一個string內容Learning的緩沖器 buf := bytes.NewBufferString("Learning") //打印為Learning fmt.Println(buf.String()) //將newString這個string寫到buf的尾部 buf.WriteString(newString) fmt.Println(buf.String()) ~~~ 打印： > ===========以下通過Write把swift寫入Learning緩沖器尾部========= Learning Learningswift ### WriteByte 將一個byte類型的數據放到緩沖器的尾部 ~~~ // WriteByte appends the byte c to the buffer, growing the buffer as needed. // The returned error is always nil, but is included to match bufio.Writer's // WriteByte. If the buffer becomes too large, WriteByte will panic with // ErrTooLarge. func (b *Buffer) WriteByte(c byte) error { b.lastRead = opInvalid m := b.grow(1) b.buf[m] = c return nil } ~~~ ~~~ fmt.Println("===========以下通過WriteByte把!寫入Learning緩沖器尾部=========") var newByte byte = '!' //創建一個string內容Learning的緩沖器 buf := bytes.NewBufferString("Learning") //打印為Learning fmt.Println(buf.String()) //將newString這個string寫到buf的尾部 buf.WriteByte(newByte) fmt.Println(buf.String()) ~~~ 打印： > ===========以下通過WriteByte把swift寫入Learning緩沖器尾部========= Learning Learning! ### WriteRune 將一個rune類型的數據放到緩沖器的尾部 ~~~ // WriteRune appends the UTF-8 encoding of Unicode code point r to the // buffer, returning its length and an error, which is always nil but is // included to match bufio.Writer's WriteRune. The buffer is grown as needed; // if it becomes too large, WriteRune will panic with ErrTooLarge. func (b *Buffer) WriteRune(r rune) (n int, err error) { if r < utf8.RuneSelf { b.WriteByte(byte(r)) return 1, nil } n = utf8.EncodeRune(b.runeBytes[0:], r) b.Write(b.runeBytes[0:n]) return n, nil } ~~~ ~~~ fmt.Println("===========以下通過WriteRune把\"好\"寫入Learning緩沖器尾部=========") var newRune = '好' //創建一個string內容Learning的緩沖器 buf := bytes.NewBufferString("Learning") //打印為Learning fmt.Println(buf.String()) //將newString這個string寫到buf的尾部 buf.WriteRune(newRune) fmt.Println(buf.String()) ~~~ 打印： > ===========以下通過WriteRune把”好”寫入Learning緩沖器尾部========= Learning Learning好 ### 完整示例 ~~~ package main import ( "bytes" "encoding/binary" "fmt" ) func main() { //newBuffer 整形轉換成字節 var n int = 10000 intToBytes := IntToBytes(n) fmt.Println("==========int to bytes========") fmt.Println(intToBytes) //NewBufferString TestBufferString() //write BufferWrite() //WriteString BufferWriteString() //WriteByte BufferWriteByte() //WriteRune BufferWriteRune() } func IntToBytes(n int) []byte { x := int32(n) //創建一個內容是[]byte的slice的緩沖器 //與bytes.NewBufferString("")等效 bytesBuffer := bytes.NewBuffer([]byte{}) binary.Write(bytesBuffer, binary.BigEndian, x) return bytesBuffer.Bytes() } func TestBufferString(){ buf1:=bytes.NewBufferString("swift") buf2:=bytes.NewBuffer([]byte("swift")) buf3:=bytes.NewBuffer([]byte{'s','w','i','f','t'}) fmt.Println("===========以下buf1,buf2,buf3等效=========") fmt.Println("buf1:", buf1) fmt.Println("buf2:", buf2) fmt.Println("buf3:", buf3) fmt.Println("===========以下創建空的緩沖器等效=========") buf4:=bytes.NewBufferString("") buf5:=bytes.NewBuffer([]byte{}) fmt.Println("buf4:", buf4) fmt.Println("buf5:", buf5) } func BufferWrite(){ fmt.Println("===========以下通過Write把swift寫入Learning緩沖器尾部=========") newBytes := []byte("swift") //創建一個內容Learning的緩沖器 buf := bytes.NewBuffer([]byte("Learning")) //打印為Learning fmt.Println(buf.String()) //將newBytes這個slice寫到buf的尾部 buf.Write(newBytes) fmt.Println(buf.String()) } func BufferWriteString(){ fmt.Println("===========以下通過Write把swift寫入Learning緩沖器尾部=========") newString := "swift" //創建一個string內容Learning的緩沖器 buf := bytes.NewBufferString("Learning") //打印為Learning fmt.Println(buf.String()) //將newString這個string寫到buf的尾部 buf.WriteString(newString) fmt.Println(buf.String()) } func BufferWriteByte(){ fmt.Println("===========以下通過WriteByte把swift寫入Learning緩沖器尾部=========") var newByte byte = '!' //創建一個string內容Learning的緩沖器 buf := bytes.NewBufferString("Learning") //打印為Learning fmt.Println(buf.String()) //將newString這個string寫到buf的尾部 buf.WriteByte(newByte) fmt.Println(buf.String()) } func BufferWriteRune(){ fmt.Println("===========以下通過WriteRune把\"好\"寫入Learning緩沖器尾部=========") var newRune = '好' //創建一個string內容Learning的緩沖器 buf := bytes.NewBufferString("Learning") //打印為Learning fmt.Println(buf.String()) //將newString這個string寫到buf的尾部 buf.WriteRune(newRune) fmt.Println(buf.String()) } ~~~ # 向 Buffer 中讀取數據 ### Read 給Read方法一個容器p，讀完后，p就滿了，緩沖器相應的減少了，返回的n為成功讀的數量 ~~~ // Read reads the next len(p) bytes from the buffer or until the buffer // is drained. The return value n is the number of bytes read. If the // buffer has no data to return, err is io.EOF (unless len(p) is zero); // otherwise it is nil. func (b *Buffer) Read(p []byte) (n int, err error) {} ~~~ ~~~ func Read(){ bufs := bytes.NewBufferString("Learning swift.") fmt.Println(bufs.String()) //聲明一個空的slice,容量為8 l := make([]byte, 8) //把bufs的內容讀入到l內,因為l容量為8,所以只讀了8個過來 bufs.Read(l) fmt.Println("::bufs緩沖器內容::") fmt.Println(bufs.String()) //空的l被寫入了8個字符,所以為 Learning fmt.Println("::l的slice內容::") fmt.Println(string(l)) //把bufs的內容讀入到l內,原來的l的內容被覆蓋了 bufs.Read(l) fmt.Println("::bufs緩沖器被第二次讀取后剩余的內容::") fmt.Println(bufs.String()) fmt.Println("::l的slice內容被覆蓋,由于bufs只有7個了,因此最后一個g被留下來了::") fmt.Println(string(l)) } ~~~ 打印： > =======Read======= Learning swift. ::bufs緩沖器內容:: swift. ::l的slice內容:: Learning ::bufs緩沖器被第二次讀取后剩余的內容:: > ::l的slice內容被覆蓋:: swift.g ### ReadByte 返回緩沖器頭部的第一個byte，緩沖器頭部第一個byte被拿掉 ~~~ // ReadByte reads and returns the next byte from the buffer. // If no byte is available, it returns error io.EOF. func (b *Buffer) ReadByte() (c byte, err error) {} ~~~ ~~~ func ReadByte(){ bufs := bytes.NewBufferString("Learning swift.") fmt.Println(bufs.String()) //讀取第一個byte,賦值給b b, _ := bufs.ReadByte() fmt.Println(bufs.String()) fmt.Println(string(b)) } ~~~ 打印： > =======ReadByte=== Learning swift. earning swift. L ### ReadRune ReadRune和ReadByte很像返回緩沖器頭部的第一個rune，緩沖器頭部第一個rune被拿掉 ~~~ // ReadRune reads and returns the next UTF-8-encoded // Unicode code point from the buffer. // If no bytes are available, the error returned is io.EOF. // If the bytes are an erroneous UTF-8 encoding, it // consumes one byte and returns U+FFFD, 1. func (b *Buffer) ReadRune() (r rune, size int, err error) {} ~~~ ~~~ func ReadRune(){ bufs := bytes.NewBufferString("學swift.") fmt.Println(bufs.String()) //讀取第一個rune,賦值給r r,z,_ := bufs.ReadRune() //打印中文"學",緩沖器頭部第一個被拿走 fmt.Println(bufs.String()) //打印"學","學"作為utf8儲存占3個byte fmt.Println("r=",string(r),",z=",z) } ~~~ ### ReadBytes ReadBytes需要一個byte作為分隔符，讀的時候從緩沖器里找第一個出現的分隔符（delim），找到后，把從緩沖器頭部開始到分隔符之間的所有byte進行返回，作為byte類型的slice，返回后，緩沖器也會空掉一部分 ~~~ // ReadBytes reads until the first occurrence of delim in the input, // returning a slice containing the data up to and including the delimiter. // If ReadBytes encounters an error before finding a delimiter, // it returns the data read before the error and the error itself (often io.EOF). // ReadBytes returns err != nil if and only if the returned data does not end in // delim. func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) {} ~~~ ~~~ func ReadBytes(){ bufs := bytes.NewBufferString("現在開始 Learning swift.") fmt.Println(bufs.String()) var delim byte = 'L' line, _ := bufs.ReadBytes(delim) fmt.Println(bufs.String()) fmt.Println(string(line)) } ~~~ 打印： > =======ReadBytes== 現在開始 Learning swift. earning swift. 現在開始 L ### ReadString ReadString需要一個byte作為分隔符，讀的時候從緩沖器里找第一個出現的分隔符（delim），找到后，把從緩沖器頭部開始到分隔符之間的所有byte進行返回，作為字符串，返回后，緩沖器也會空掉一部分和ReadBytes類似 ~~~ // ReadString reads until the first occurrence of delim in the input, // returning a string containing the data up to and including the delimiter. // If ReadString encounters an error before finding a delimiter, // it returns the data read before the error and the error itself (often io.EOF). // ReadString returns err != nil if and only if the returned data does not end // in delim. func (b *Buffer) ReadString(delim byte) (line string, err error) {} ~~~ ### ReadFrom 從一個實現io.Reader接口的r，把r里的內容讀到緩沖器里，n返回讀的數量 ~~~ // ReadFrom reads data from r until EOF and appends it to the buffer, growing // the buffer as needed. The return value n is the number of bytes read. Any // error except io.EOF encountered during the read is also returned. If the // buffer becomes too large, ReadFrom will panic with ErrTooLarge. func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {} ~~~ ~~~ func ReadFrom(){ //test.txt 內容是 "未來" file, _ := os.Open("learngo/bytes/text.txt") buf := bytes.NewBufferString("Learning swift.") buf.ReadFrom(file) //將text.txt內容追加到緩沖器的尾部 fmt.Println(buf.String()) } ~~~ 打印： > =======ReadFrom=== Learning swift.未來 ### Reset 將數據清空，沒有數據可讀 ~~~ // Reset resets the buffer so it has no content. // b.Reset() is the same as b.Truncate(0). func (b *Buffer) Reset() { b.Truncate(0) } ~~~ ~~~ func Reset(){ bufs := bytes.NewBufferString("現在開始 Learning swift.") fmt.Println(bufs.String()) bufs.Reset() fmt.Println("::已經清空了bufs的緩沖內容::") fmt.Println(bufs.String()) } ~~~ 打印： > =======Reset====== 現在開始 Learning swift. ::已經清空了bufs的緩沖內容:: ### string 將未讀取的數據返回成 string ~~~ // String returns the contents of the unread portion of the buffer // as a string. If the Buffer is a nil pointer, it returns "<nil>". func (b *Buffer) String() string {} ~~~