func main() {
 r, _ := os.Open("test.txt")
 w, _ := os.Create("write.txt")
 num, err := io.Copy(w, w)
 if err != nil {
  fmt.Println(err)
 }
 fmt.Println(num) //返回int64的11 打開我的write.txt正是test.txt里邊的hello widuu
} 

func main() {
 r, _ := os.Open("test.txt")
 w, _ := os.Create("write1.txt")
 num, err := io.CopyN(w, r, 5)
 if err != nil {
  fmt.Println(err)
 }
 defer r.Close()
 b, _ := ioutil.ReadFile("write1.txt")
 fmt.Println(string(b)) //輸出 hello
 fmt.Println(num)       //5
}

func main() {
 r, _ := os.Open("write1.txt")
 b := make([]byte, 20)
 defer r.Close()
 var total int
 for {
  n, err := io.ReadAtLeast(r, b, 8)
  if err == nil {
   fmt.Println("Read enough value:", string(b)) // Read enough value: hello widuu
  }
  if err == io.ErrUnexpectedEOF { //讀取了的數(shù)據(jù)小于我們限定的最小讀取數(shù)據(jù)8
   fmt.Println("Read fewer value:", string(b[0:n]))
  }
  
  if err == io.ErrShortBuffer{   //這個(gè)是我們設(shè)定的buf也就是b小于我們限定8
   fmt.Println("buf too Short")
   os.Exit(1)
  }
  if err == io.EOF { //讀完了 輸出
   fmt.Println("Read end total", total) //Read end total 11
   break
  }
  total = total + n
 }
}

import (
 "fmt"
 "io"
 "os"
)

func main() {
 r, _ := os.Open("write.txt")
 b := make([]byte, 20)
 num, err := io.ReadFull(r, b)
 defer r.Close()
 if err == io.EOF {
  fmt.Println("Read end total", num)
 }
 if err == io.ErrUnexpectedEOF {
  fmt.Println("Read fewer value:", string(b[:num])) //Read fewer value: hello widuu，依然是buf長度大于讀取的長度
  return
 }

 fmt.Println("Read  value:", string(b)) //如果b是5 就出現(xiàn)這里
}

type Writer interface {
    Write(p []byte) (n int, err error)
}
跟read一樣我們的*File是有func (f *File) Write(b []byte) (n int, err error)，當(dāng)然其實(shí)我們的*File中就已經(jīng)有WirteString了func (f *File) WriteString(s string) (ret int, err error)
import (
 "fmt"
 "io"
 "io/ioutil"
 "os"
)

func main() {
 w, _ := os.OpenFile("write1.txt", os.O_RDWR, os.ModePerm)
 n, err := io.WriteString(w, "ni hao ma")
 if err != nil {
  fmt.Println(err) //當(dāng)我用os.open()的時(shí)候木有權(quán)限  悲催的~~輸出write write1.txt: Access is denied.
 }
 defer w.Close()
 b, _ := ioutil.ReadFile("write1.txt")
 fmt.Println("write total", n) //write total 9
 fmt.Println(string(b))        // ni hao ma
}

type LimitedReader struct {
    R Reader // 讀取器了
    N int64  // 最大字節(jié)限制
}

func main() {
 reader, _ := os.Open("test.txt")
 limitedreader := io.LimitedReader{
  R: reader,
  N: 20,
 }
 p := make([]byte, 10)
 var total int
 for {
  n, err := limitedreader.Read(p)
  if err == io.EOF {
   fmt.Println("read total", total)     //read total 11
   fmt.Println("read value", string(p)) //read value hello widuu
   break
  }
  total = total + n

 }

}

import (
 "fmt"
 "io"
 "reflect"
)

func main() {
 r, w := io.Pipe()
 fmt.Println(reflect.TypeOf(r)) //*io.PipeReader
 fmt.Println(reflect.TypeOf(w)) //*io.PipeWriter
}

func main() {
 r, w := io.Pipe()
 r.Close()

 _, err := w.Write([]byte("hello widuu")) 

 if err == io.ErrClosedPipe {
  fmt.Println("管道已經(jīng)關(guān)閉無法寫入") //管道已經(jīng)關(guān)閉無法寫入
 }
}

import (
 "errors"
 "fmt"
 "io"
)

func main() {
 r, w := io.Pipe()
 r.Close()
 err := errors.New("管道符關(guān)閉了") //errors這個(gè)包我們前邊已經(jīng)說過了，就一個(gè)方法New不會(huì)的可以看看前邊的
 r.CloseWithError(err)
 _, err = w.Write([]byte("test"))
 if err != nil {
  fmt.Println(err) //管道符關(guān)閉了
 }
}

func main() {
 r, w := io.Pipe()
 go w.Write([]byte("hello widuu"))
 d := make([]byte, 11)
 n, _ := r.Read(d) //從管道里讀取數(shù)據(jù)
 fmt.Println(string(d))
 fmt.Println(n)
}