Go language basic file reading Read os package

os.Open()-->return value *File, err ***** can be opened after opening

File.Read([]byte)-->count,err, read data, after reading err will display EOF to prove that the entire file is read,

Don't forget to close the file after opening it

You can use defer to delay the final shutdown

derer File.close closes the file

package main

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

func main()  {
   file,err:= os.Open("C:\\liu\\pro\\aa.txt")
   if err!=nil{
      fmt.Println( "Failed to open the file.." )
       return
    }
    defer file.Close()
    //Read data
    bs := make ([] byte , 4 )
   count := 0 //The number of each read
 for {   
      count, err = file.Read(bs)
      if err ==io.EOF{
         fmt.Println()
         fmt.Println( "Data read complete.." )
          break
       }
      fmt.Print(string(bs[:count]))
   }


   /*
    //For the first read, read the corresponding file through file, read the data into bs, the return value is the actual number
    count read this time, err = file.Read(bs)
    fmt.Println( err) //<nil>
    fmt.Println(count) //4
    fmt.Println(bs) //[97 98 99 100]
    fmt.Println(string(bs)) //abcd
    //The second read
    count ,err = file.Read(bs)
    fmt.Println(err) //<nil>
    fmt.Println(count) //4
    fmt.Println(bs) //[101 102 103 104]
    fmt.Println(string(bs )) //efgh
    //The third read, read 2
    counts, err = file.Read(bs)
    fmt.Println(err) //<nil>
    fmt.Println(count) //2
    fmt.Println( bs) //[101 102 103 104]
    //fmt.Println(string(bs)) //efgh ijgh
    fmt.Println(string(bs[:count])) //ij


   //For the fourth read, when the end of the file is read, the error returned is io.EOF, and the value of count is 0
    count, err= file.Read(bs)
    fmt.Println(err) //EOF
    fmt. Println(count) //0
 }
   

File.ReadAt([] byte, off)-->coutn,err, read from the specified off position

package main

import (
   "os"
   "fmt"
)

func main () {
    /*
    Read([]bs), read from the beginning by default, the
      cursor
 is at the end, read again, the return error is io.EOF    ReadAt([] bs, offset int), read from the specified position
     * /
     file , _:=os.Open( "C:\\liu\\pro\\aa.txt" )
    bs := make([] byte ,4)
    /*
    1.ReadAt(bs, 0)-->4
    2.ReadAt(bs,4)-->4
    3.ReadAt(bs,8)-->2    EOF
     */
    count, err:=file.ReadAt(bs,2)
    fmt.Println(err) //<nil>
    fmt.Println(count) //4
    fmt.Println(string(bs[0:count]))

    count, err = file.ReadAt(bs,7)
    fmt.Println(err) //EOF
    fmt.Println(count) //3
    fmt.Println(string(bs[:count]))
}