[go ~ 0 to 1] read, write and create files on the sixth day

1. Opening and closing of files

1.1 os.open

os.open Function can open a file call close() Method Close file

	// Open file 
	open, err := os.Open("./1.text")
	
	if err != nil {
		// Print exception information 
		fmt.Println("open file err", err)
	}

	fmt.Println(" File acquisition completed ")

	// No exception occurred , Close file 
	open.Close()

To prevent forgetting to close the file , Usually, the code to close the file is written in defer in

	// Open file 
	open, err := os.Open("./1.text")

	defer func() {
		if open != nil {
			//  Close file 
			open.Close()
		}
	}()

	if err != nil {
		// Print exception information 
		fmt.Println("open file err", err)
	}

	fmt.Println(" File acquisition completed ")

1.2 os.OpenFile() Open file in specified mode

func OpenFile(name string, flag int, perm FileMode) (*File, error) {
	...
}

among ：

name： The name of the file to open flag： Open file mode . There are several modes ：

Pattern	meaning
os.O_WRONLY	Just write
os.O_CREATE	create a file
os.O_RDONLY	read-only
os.O_RDWR	Reading and writing
os.O_TRUNC	Empty
os.O_APPEND	Additional

perm： File permissions , An octal number .r（ read ）04,w（ Write ）02,x（ perform ）01.

2. File reading

2.1 Read the data in the file by opening the file

// First you need to open a file 
	open, err := os.Open("./1.text")
	defer func() {
		e := recover()
		if e != nil {

			fmt.Println(" An exception occurred when opening the file ", e)
		}
	}()

	if err != nil {
		//  If there is any abnormality    There's no need to go down    Throw out 
		panic(err)
	}

	// If there is no abnormality 
	// establish   Byte slice 
	bytes := make([]byte, 1024)

	defer func() {
		e := recover()
		if e != nil {

			fmt.Println(" An exception occurred while reading the file ", e)
		}
	}()

	for {
		// Circle reading 
		_, err := open.Read(bytes)

		if err != nil {
			panic(err)
		}

		// Print the results 
		fmt.Println(string(bytes))
	}

2.2 Use bufio Read the whole line of the file

bufio Is in file It encapsulates a layer of API , Support more functions

	// Similarly, first open a file 
	file, err := os.Open("./1.text")

	defer recover()

	if err != nil {
		panic(" An exception occurred while opening the file ")
	}

	//  Encapsulated in the  bufio
	reader := bufio.NewReader(file)

	defer recover()

	for {

		// Read the specified string and change to another line 
		line, _, err := reader.ReadLine()

		if err != nil {
			if err == io.EOF {
				fmt.Println(" The file is read and written ")
				break
			}
			panic(" File reading exception ")
		}

		fmt.Println(string(line))
	}

	fmt.Println(" End of program running ")
func main() {
	file, err := os.OpenFile("xx.txt", os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0666)
}

2.3 ioutil Read the entire file at once

3. Write file operation

Whether it is file reading or file writing You need to open the file first Do it again

3.1 file.Write And file.WriteString

//  So let's open the file   O_RDWR   read-write permission   O_TRUNC   Empty files   0  Start with octal  666 Express   Current user   Current group    Other users   Read and write permissions 
	file, err := os.OpenFile("1.text", os.O_RDWR|os.O_TRUNC, 0666)
	if err != nil {
		fmt.Printf(" Exception in opening file  %v", err)
	}

	defer file.Close()

	//  return   Bytes written 
	write, err := file.Write([]byte(" Test file write  \n"))
	file.WriteString(" Write the entire string at once ")

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

	fmt.Println(write)

3.2 bufio.NewWriter

Use bufio Be sure to call refresh

//  Based on cache operation 
	file, err := os.OpenFile("2.text", os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0666)
	if err != nil {
		panic(err)
	}

	defer func() {
		file.Close()
		if e := recover(); e != nil {
			fmt.Printf(" abnormal  :  Exception in opening file  %v", e)
		}
	}()

	//  Use  bufio  Based on cache operation io flow 
	//  Need to   One  io  Interface package  Writer  Interface implementation class   and  file  It's time to   Method 

	writer := bufio.NewWriter(file)

	writer.WriteString("  Write cache string contents  2")

	// You need to refresh the data in the cache to the hard disk 
	writer.Flush()

3.3 ioUtil Tool class

	//  Use tool class    Open file , Write the file at one go 
	err := ioutil.WriteFile("3.text", []byte(" Tool class writes content "), 0666)

	if err != nil {
		fmt.Println(" The program runs abnormally ", err)
	}