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章节9_03_Reader

一.输入流

  • 流(stream)是应用程序和外部资源进行数据交互的纽带
  • 流分为输入流和输出流,输入和输出都是相对于程序,把外部数据传入到程序中叫做输入,反之叫做输出流
  • 输入流(Input Stream),输入流(Output Stream) 平时所说的I/O流
  • 在Go语言标准库中io包下是Reader接口表示输入流,只要实现这个接口就属于输入流
// Reader is the interface that wraps the basic Read method.
//
// Read reads up to len(p) bytes into p. It returns the number of bytes
// read (0 <= n <= len(p)) and any error encountered. Even if Read
// returns n < len(p), it may use all of p as scratch space during the call.
// If some data is available but not len(p) bytes, Read conventionally
// returns what is available instead of waiting for more.
//
// When Read encounters an error or end-of-file condition after
// successfully reading n > 0 bytes, it returns the number of
// bytes read. It may return the (non-nil) error from the same call
// or return the error (and n == 0) from a subsequent call.
// An instance of this general case is that a Reader returning
// a non-zero number of bytes at the end of the input stream may
// return either err == EOF or err == nil. The next Read should
// return 0, EOF.
//
// Callers should always process the n > 0 bytes returned before
// considering the error err. Doing so correctly handles I/O errors
// that happen after reading some bytes and also both of the
// allowed EOF behaviors.
//
// Implementations of Read are discouraged from returning a
// zero byte count with a nil error, except when len(p) == 0.
// Callers should treat a return of 0 and nil as indicating that
// nothing happened; in particular it does not indicate EOF.
//
// Implementations must not retain p.
type Reader interface {
    Read(p []byte) (n int, err error)
}

二.代码演示

  • 可以使用strings包下的NewReader创建字符串流
    r := strings.NewReader("hello 世界")
    b := make([]byte, r.Size())//创建字节切片,存放流中数据,根据流数据大小创建切片大小
    n, err := r.Read(b)//把流中数据读取到切片中
    if err != nil {
        fmt.Println("读取失败,", err)
        return
    }
    fmt.Println("读取数据长度,", n)

    fmt.Println("流中数据",string(b))//以字符串形式输入切片中数据
  • 最常用的是文件流,把外部文件中数据读取到程序中
    f, err := os.Open("D:/go.txt")//打开文件
    defer f.Close()
    if err != nil {
        fmt.Println("文件读取失败,", err)
        return
    }
    fileInfo, err := f.Stat()//获取文件信息
    if err != nil {
        fmt.Println("文件信息获取失败,", err)
        return
    }
    b := make([]byte, fileInfo.Size())//根据文件中数据大小创建切片
    _, err = f.Read(b)//读取数据到切片中
    if err != nil {
        fmt.Println("文件流读取失败:", err)
        return
    }
    fmt.Println("文件中内容为:", string(b))//以字符串形式输入切片中数据

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