Examples illustrate the common use of the Go library functions in the Go language

(f *File).Name() this function is to return the name of the file, function prototype func (f *File) Name() string to the file pointer operation, return a string, feel the chicken helper method underlying implementation

 func (f *File) Name() string { return f.name }

 import (

 "fmt"

 "os"

)
func main() {

 f, _ := os.Open("1.go")

 fmt.Println(f.Name()) // The output 1.go

}

(f *File).Read() this is the function pointer to operate, belongs to method *FIlE, function prototype func (f *File) Read(b []byte) (n int, err error) input the number of bytes read, return the length of the bytes and error information

import (

 "fmt"

 "os"

)
func main() {

 b := make([]byte, 100) // Sets the number of bytes read 

 f, _ := os.Open("11.go")

 n, _ := f.Read(b)

 fmt.Println(n) 

 fmt.Println(string(b[:n])) // output   Why is it n Instead of typing directly 100 ? The underlying implementation is this way 

 /*

  n, e := f.read(b)

     if n < 0 {

       n = 0

     }

  if n == 0 && len(b) > 0 && e == nil {

     return 0, io.EOF

    }

   */

   // So not enough bytes 100 Just read n

}

The prototype of this function is func (f *File) ReadAt(b []byte, off int64) (n int, err error) with the subscript added, you can customize how much you read

import (

 "fmt"

 "os"

)
func main() {

 f, _ := os.Open("11.go")

 b := make([]byte, 20)

 n, _ := f.ReadAt(b, 15)

 fmt.Println(n)

 fmt.Println(string(b[:n]))

}

(f *File).Readdir() function prototype func (f *File) Readdir(n int) (fi []FileInfo, err error), we want to open a folder, and then set the number of folder files to read, and return the fileinfo information of the file

import (

 "fmt"

 "os"

)
func main() {

 f, err := os.Open("src") // Open the 1 A directory 

 if err != nil {

  fmt.Println(err)

 }

 defer f.Close()

 ff, _ := f.Readdir(10)    // Sets the number of reads  <=0 Is to read all the files   The returned []fileinfo

 for i, fi := range ff {

  fmt.Printf("filename %d: %+v\n", i, fi.Name())  // We output the name of the file 

 }

}

(f *File).Readdirnames is a function that reads the file name in the directory. In fact, we have already realized the function function of the last function, the prototype of the function func (f *File) Readdirnames(n int) (names []string, err error)

import (

 "fmt"

 "os"

)
func main() {

 f, _ := os.Open("bin")

 names, err := f.Readdirnames(0)

 if err != nil {

  fmt.Println(err)

 }

 for i, name := range names {

  fmt.Printf("filename %d: %s\n", i, name)

 }

}

f *File).Seek() is the address of the offset pointer. The prototype of the function is func (f *File). Seek(offset int64, whence int). 2 represents the position relative to the end of the file. ret returns the current position of the pointer

import (

 "fmt"

 "os"

)
func main() {

 b := make([]byte, 10)

 f, _ := os.Open("1.go")

 defer f.Close()

 f.Seek(1, 0)    // It's the same thing as the starting offset 1

 n, _ := f.Read(b)

 fmt.Println(string(b[:n]))  // The original character package  The output ackage

}

The function prototype func (f *File) Write(b []byte) (n int, err error) returns the number of bytes written by n

import (

 "fmt"

 "os"

)
func main() {

 f, _ := os.OpenFile("1.go", os.O_RDWR|os.O_APPEND, 0755) // Open the file by appending and reading and writing 

 n, _ := f.Write([]byte("helloword"))                     // We write hellword

 fmt.Println(n)                                           // The number of bytes printed to write 

 b := make([]byte, 20)

 f.Seek(0, 0)            // Pointer back to 0

 data, _ := f.Read(b)

 fmt.Println(string(b[:data]))        // The output packagehelloword

}

The function prototype is func (f *File) WriteAt(b []byte, off int64) (n int, err error). The return value is the same

import (

 "fmt"

 "os"

)
func main() {

 f, _ := os.OpenFile("1.go", os.O_RDWR, os.ModePerm)

 f.WriteAt([]byte("widuu"), 10) // In the offset 10 Where to write 

 b := make([]byte, 20)

 d, _ := f.ReadAt(b, 10)    // The offset 10 The place to start reading 

 fmt.Println(string(b[:d])) //widuudhellowordhello

}

func (f *File) WriteString(s string) (ret int, err error

import (

 "fmt"

 "os"

)
func main() {

 f, _ := os.OpenFile("2.go", os.O_RDWR, os.ModePerm)

 n, _ := f.WriteString("hello word widuu") // Write string 

 fmt.Println(n)

 b := make([]byte, n)

 f.Seek(0, 0)    //1 You must return the offset address 0 Otherwise, 1 Right at the end of the write 

 c, _ := f.Read(b)

 fmt.Println(string(b[:c])) // return hello word widuu

}