淺談Golang是如何讀取文件內(nèi)容的(7種)

package main


import (
 "os"
 "fmt"
)
func main() {
 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))
}

package main


import (
 "io"
 "os"
 "fmt"
)

const BufferSize = 100

func main() {
 
 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]))
 }
}

package main

import (
 "fmt"
 "os"
 "sync"
)

const BufferSize = 100

type chunk struct {
 bufsize int
 offset int64
}

func main() {
 
 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
 // buffer sizes that each of the go routine below should use. ReadAt
 // returns an error if the buffer size is larger than the bytes returned
 // from the file.
 chunksizes := make([]chunk, concurrency)

 // All buffer sizes are the same in the normal case. Offsets depend on the
 // index. Second go routine should start at 100, for example, given our
 // buffer size of 100.
 for i := 0; i  concurrency; i++ {
 chunksizes[i].bufsize = BufferSize
 chunksizes[i].offset = int64(BufferSize * i)
 }

 // check for any left over bytes. Add the residual number of bytes as the
 // the last chunk size.
 if remainder := filesize % BufferSize; remainder != 0 {
 c := chunk{bufsize: remainder, offset: int64(concurrency * BufferSize)}
 concurrency++
 chunksizes = append(chunksizes, c)
 }

 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)

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

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

 wg.Wait()
}

package main

import (
 "fmt"
 "os"
 "bufio"
)

const BufferSize = 100

type chunk struct {
 bufsize int
 offset int64
}

func main() {
 file, err := os.Open("filetoread.txt")
 if err != nil {
 fmt.Println(err)
 return
 }
 defer file.Close()
 scanner := bufio.NewScanner(file)
 scanner.Split(bufio.ScanLines)

 // Returns a boolean based on whether there's a next instance of `\n`
 // character in the IO stream. This step also advances the internal pointer
 // to the next position (after '\n') if it did find that token.
 for {
 read := scanner.Scan()
 if !read {
  break
  
 }
 fmt.Println("read byte array: ", scanner.Bytes())
 fmt.Println("read string: ", scanner.Text())
 }
 
}

package main

import (
 "bufio"
 "fmt"
 "os"
)

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

 scanner := bufio.NewScanner(file)
 scanner.Split(bufio.ScanLines)

 // This is our buffer now
 var lines []string

 for scanner.Scan() {
 lines = append(lines, scanner.Text())
 }

 fmt.Println("read lines:")
 for _, line := range lines {
 fmt.Println(line)
 }
}

package main

import (
 "bufio"
 "fmt"
 "os"
)

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

 scanner := bufio.NewScanner(file)
 scanner.Split(bufio.ScanWords)

 var words []string

 for scanner.Scan() {
 words = append(words, scanner.Text())
 }

 fmt.Println("word list:")
 for _, word := range words {
 fmt.Println(word)
 }
}

package main

import (
 "bufio"
 "fmt"
 "os"
)

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

 scanner := bufio.NewScanner(file)
 scanner.Split(bufio.ScanWords)

 // initial size of our wordlist
 bufferSize := 50
 words := make([]string, bufferSize)
 pos := 0

 for scanner.Scan() {
 if err := scanner.Err(); err != nil {
  // This error is a non-EOF error. End the iteration if we encounter
  // an error
  fmt.Println(err)
  break
 }

 words[pos] = scanner.Text()
 pos++

 if pos >= len(words) {
  // expand the buffer by 100 again
  newbuf := make([]string, bufferSize)
  words = append(words, newbuf...)
 }
 }

 fmt.Println("word list:")
 // we are iterating only until the value of "pos" because our buffer size
 // might be more than the number of words because we increase the length by
 // a constant value. Or the scanner loop might've terminated due to an
 // error prematurely. In this case the "pos" contains the index of the last
 // successful update.
 for _, word := range words[:pos] {
 fmt.Println(word)
 }
}

package main

import (
 "bufio"
 "fmt"
 "strings"
)

func main() {
 longstring := "This is a very long string. Not."
 var words []string
 scanner := bufio.NewScanner(strings.NewReader(longstring))
 scanner.Split(bufio.ScanWords)

 for scanner.Scan() {
 words = append(words, scanner.Text())
 }

 fmt.Println("word list:")
 for _, word := range words {
 fmt.Println(word)
 }
}

type SplitFunc func(data []byte, atEOF bool) (advance int, token []byte, err error)

package main

import (
 "bufio"
 "bytes"
 "fmt"
 "strings"
)

func main() {
 csvstring := "name, age, occupation"

 // An anonymous function declaration to avoid repeating main()
 ScanCSV := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
 commaidx := bytes.IndexByte(data, ',')
 if commaidx > 0 {
  // we need to return the next position
  buffer := data[:commaidx]
  return commaidx + 1, bytes.TrimSpace(buffer), nil
 }

 // if we are at the end of the string, just return the entire buffer
 if atEOF {
  // but only do that when there is some data. If not, this might mean
  // that we've reached the end of our input CSV string
  if len(data) > 0 {
  return len(data), bytes.TrimSpace(data), nil
  }
 }

 // when 0, nil, nil is returned, this is a signal to the interface to read
 // more data in from the input reader. In this case, this input is our
 // string reader and this pretty much will never occur.
 return 0, nil, nil
 }

 scanner := bufio.NewScanner(strings.NewReader(csvstring))
 scanner.Split(ScanCSV)

 for scanner.Scan() {
 fmt.Println(scanner.Text())
 }
}

package main

import (
 "io/ioutil"
 "log"
 "fmt"
)

func main() {
 bytes, err := ioutil.ReadFile("filetoread.txt")
 if err != nil {
 log.Fatal(err)
 }

 fmt.Println("Bytes read: ", len(bytes))
 fmt.Println("String read: ", string(bytes))
}

package main

import (
 "io/ioutil"
 "log"
 "fmt"
)

func main() {
 filelist, err := ioutil.ReadDir(".")
 if err != nil {
 log.Fatal(err)
 }
 for _, fileinfo := range filelist {
 if fileinfo.Mode().IsRegular() {
  bytes, err := ioutil.ReadFile(fileinfo.Name())
  if err != nil {
  log.Fatal(err)
  }
  fmt.Println("Bytes read: ", len(bytes))
  fmt.Println("String read: ", string(bytes))
 }
 }
}