GoLang 读文件方法

• 将文件内容全部读入内存

file, err := os.Open("filetoread.txt")
if err != nil {
  fmt.Println(err)
  return
}
defer file.Close()

fileinfo, err := file.Stat()
if err != nil {
  fmt.Println(err)
  return
}

filesize := fileinfo.Size()
buffer := make([]byte, filesize)

bytesread, err := file.Read(buffer)
if err != nil {
  fmt.Println(err)
  return
}

fmt.Println("bytes read: ", bytesread)
fmt.Println("bytestream to string: ", string(buffer))

• 一块一块的读文件

const BufferSize = 100
file, err := os.Open("filetoread.txt")
if err != nil {
  fmt.Println(err)
  return
}
defer file.Close()

buffer := make([]byte, BufferSize)

for {
  bytesread, err := file.Read(buffer)

  if err != nil {
    if err != io.EOF {
      fmt.Println(err)
    }

    break
  }

  fmt.Println("bytes read: ", bytesread)
  fmt.Println("bytestream to string: ", string(buffer[:bytesread]))
}

• 按块并发读文件

const BufferSize = 100
file, err := os.Open("filetoread.txt")
if err != nil {
  fmt.Println(err)
  return
}
defer file.Close()

fileinfo, err := file.Stat()
if err != nil {
  fmt.Println(err)
  return
}

filesize := int(fileinfo.Size())
// Number of go routines we need to spawn.
concurrency := filesize / BufferSize

// check for any left over bytes. Add one more go routine if required.
if remainder := filesize % BufferSize; remainder != 0 {
  concurrency++
}

var wg sync.WaitGroup
wg.Add(concurrency)

for i := 0; i < concurrency; i++ {
  go func(chunksizes []chunk, i int) {
    defer wg.Done()

    chunk := chunksizes[i]
    buffer := make([]byte, chunk.bufsize)
    bytesread, err := file.ReadAt(buffer, chunk.offset)

    // As noted above, ReadAt differs slighly compared to Read when the
    // output buffer provided is larger than the data that's available
    // for reading. So, let's return early only if the error is
    // something other than an EOF. Returning early will run the
    // deferred function above
    if err != nil && err != io.EOF {
      fmt.Println(err)
      return
    }

    fmt.Println("bytes read, string(bytestream): ", bytesread)
    fmt.Println("bytestream to string: ", string(buffer[:bytesread]))
  }(chunksizes, i)
}

wg.Wait()

• Scanning方式读文件

参考原文：Golang: Reading files in Go — an overview