golang標準庫學習———bytes.Buffer
阿新 • • 發佈：2022-03-16
轉自：Golang bytes.buffer詳解 - salami-china - 部落格園 (cnblogs.com)
Buffer 是 bytes 包中的一個 type Buffer struct{…}
（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（存取資料）
建立緩衝器
func main() {
buf1 := bytes.NewBufferString("hello")
buf2 := bytes.NewBuffer([]byte("hello"))
buf3 := bytes.NewBuffer([]byte{'h','e','l','l','o'})
fmt.Printf("%v,%v,%v\n",buf1,buf2,buf3)
fmt.Printf("%v,%v,%v\n",buf1.Bytes(),buf2.Bytes(),buf3.Bytes())
buf4 := bytes.NewBufferString("")
buf5 := bytes.NewBuffer([]byte{})
fmt.Println(buf4.Bytes(),buf5.Bytes())
}
輸出
hello,hello,hello [104 101 108 108 111],[104 101 108 108 111],[104 101 108 108 111] [] []
寫入到緩衝器
buffer在new的時候是空的，也是可以直接Write的
Write
func (b *Buffer) Write(p []byte) (n int,err error)
func main() {
s := []byte(" world")
buf := bytes.NewBufferString("hello")
fmt.Printf("%v,%v\n",buf.String(),buf.Bytes())
buf.Write(s)
fmt.Printf("%v,%v\n",buf.String(),buf.Bytes())
}
結果
hello,[104 101 108 108 111] hello world,[104 101 108 108 111 32 119 111 114 108 100]
WriteString
func (b *Buffer) WriteString(s string)(n int,err error)
func main() {
s := " world"
buf := bytes.NewBufferString("hello")
fmt.Printf("%v,%v\n",buf.String(),buf.Bytes())
buf.WriteString(s)
fmt.Printf("%v,%v\n",buf.String(),buf.Bytes())
}
結果
hello,[104 101 108 108 111] hello world,[104 101 108 108 111 32 119 111 114 108 100]
緩衝區原理介紹
go位元組緩衝區底層以位元組切片做儲存，切片存在長度 len 與容量 cap, 緩衝區寫從長度len的位置開始寫，當len>cap時，會自動擴容。緩衝區讀會從內建標記off位置開始讀(off始終記錄讀的起始位置)，當off==len時，表明緩衝區已全部讀完
並重置緩衝區(len=off=0),此外當將要內容長度+已寫的長度(即len) <= cap/2時，緩衝區前移覆蓋掉已讀的內容(off=0，len-=off)，從避免緩衝區不斷擴容
func main() {
byteSlice := make([]byte, 20)
byteSlice[0] = 1 // 將緩衝區第一個位元組置1
byteBuffer := bytes.NewBuffer(byteSlice) // 建立20位元組緩衝區 len = 20 off = 0
c, _ := byteBuffer.ReadByte() // off+=1
fmt.Printf("len:%d, c=%d\n", byteBuffer.Len(), c) // len = 20 off =1 列印c=1
byteBuffer.Reset() // len = 0 off = 0
fmt.Printf("len:%d\n", byteBuffer.Len()) // 列印len=0
byteBuffer.Write([]byte("hello byte buffer")) // 寫緩衝區 len+=17
fmt.Printf("len:%d\n", byteBuffer.Len()) // 列印len=17
byteBuffer.Next(4) // 跳過4個位元組 off+=4
c, _ = byteBuffer.ReadByte() // 讀第5個位元組 off+=1
fmt.Printf("第5個位元組:%d\n", c) // 列印:111(對應字母o) len=17 off=5
byteBuffer.Truncate(3) // 將未位元組數置為3 len=off+3=8 off=5
fmt.Printf("len:%d\n", byteBuffer.Len()) // 列印len=3為未讀位元組數 上面len=8是底層切片長度
byteBuffer.WriteByte(96) // len+=1=9 將y改成A
byteBuffer.Next(3) // len=9 off+=3=8
c, _ = byteBuffer.ReadByte() // off+=1=9 c=96
fmt.Printf("第9個位元組:%d\n", c) // 列印:96
}
demo1
package main
import "bytes"
import "log"
func main(){
buf := &bytes.Buffer{}
buf.WriteString("abcdefg")
str, _ := buf.ReadString('?')
log.Println("str = ", str)
log.Println("buff = ", buf.String())
}
輸出
[root@localhost]# go run buffer.go 2020/06/05 19:12:42 str = abcdefg 2020/06/05 19:12:42 buff =
demo2
// MyBuffer2 project main.go
package main
import (
"bytes"
"log"
"os"
)
func main() {
log.SetFlags(log.Lshortfile)
buff := bytes.NewBufferString("123456789")
log.Println("buff = ", buff.String())
s := make([]byte, 4)
n, _ := buff.Read(s)
log.Println("buff = ", buff.String())
log.Println("s = ", string(s))
log.Println("n = ", n)
n, _ = buff.Read(s)
log.Println("buff = ", buff.String())
log.Println("s = ", string(s))
log.Println("n = ", n)
n, _ = buff.Read(s)
log.Println("buff = ", buff.String())
log.Println("s = ", string(s))
log.Println("n = ", n)
buff.Reset()
buff.WriteString("abcdefg")
log.Println("buff = ", buff.String())
b, _ := buff.ReadByte()
log.Println("b = ", string(b))
log.Println("buff = ", buff.String())
b, _ = buff.ReadByte()
log.Println("b = ", string(b))
log.Println("buff = ", buff.String())
bs, _ := buff.ReadBytes('e')
log.Println("bs = ", string(bs))
log.Println("buff = ", buff.String())
buff.Reset()
buff.WriteString("編譯輸出GO")
r, l, _ := buff.ReadRune()
log.Println("r = ", r, ", l = ", l, ", string(r) = ", string(r))
buff.Reset()
buff.WriteString("qwer")
str, _ := buff.ReadString('?')
log.Println("str = ", str)
log.Println("buff = ", buff.String())
buff.WriteString("qwer")
str, _ = buff.ReadString('w')
log.Println("str = ", str)
log.Println("buff = ", buff.String())
file, _ := os.Open("doc.go")
buff.Reset()
buff.ReadFrom(file)
log.Println("doc.go = ", buff.String())
buff.Reset()
buff.WriteString("中國人")
cbyte := buff.Bytes()
log.Println("cbyte = ", cbyte)
}
輸出：
C:/Go/bin/go.exe build -i [D:/golang/src/MyBuffer2] 成功: 程序退出程式碼 0. D:/golang/src/MyBuffer2/MyBuffer2.exe [D:/golang/src/MyBuffer2] main.go:13: buff = 123456789 main.go:17: buff = 56789 main.go:18: s = 1234 main.go:19: n = 4 main.go:22: buff = 9 main.go:23: s = 5678 main.go:24: n = 4 main.go:27: buff = main.go:28: s = 9678 main.go:29: n = 1 main.go:33: buff = abcdefg main.go:36: b = a main.go:37: buff = bcdefg main.go:40: b = b main.go:41: buff = cdefg main.go:44: bs = cde main.go:45: buff = fg main.go:50: r = 32534 , l = 3 , string(r) = 編 main.go:55: str = qwer main.go:56: buff = main.go:60: str = qw main.go:61: buff = er main.go:66: doc.go = // MyBuffer2 project doc.go /* MyBuffer2 document */ package main main.go:71: cbyte = [228 184 173 229 155 189 228 186 186] 成功: 程序退出程式碼 0.