Golang reading and writing files

read file

There are three ways to read files:

• Read the entire file into memory
• Read by bytes
• Read by line

The specific implementation is as follows:

package main import ( "os" "io/ioutil" "fmt" ) func main() { file, err := os.Open("D:/gopath/src/golang_development_notes/example/log.txt") if err != nil { panic(err) } defer file.Close() content, err := ioutil.ReadAll(file) fmt.Println(string(content)) }

perhaps

package main import ( "os" "io/ioutil" "fmt" ) func main() { filepath := "D:/gopath/src/golang_development_notes/example/log.txt" content ,err :=ioutil.ReadFile(filepath) if err !=nil { panic(err) } fmt.Println(string(content)) }

Read the whole file into memory, which is more efficient and occupies the most memory.

2. Read file by byte

package main import ( "bufio" "fmt" "io" "io/ioutil" "os" ) func main() { filepath := "D:/gopath/src/golang_development_notes/example/log.txt" fi, err := os.Open(filepath) if err != nil { panic(err) } defer fi.Close() r := bufio.NewReader(fi) chunks := make([]byte, 0) buf := make([]byte, 1024) //How many bytes are read at a time for { n, err := r.Read(buf) if err != nil && err != io.EOF { panic(err) } fmt.Println(string(buf[:n])) break if 0 == n { break } chunks = append(chunks, buf[:n]...) } fmt.Println(string(chunks)) }

or

package main import ( "fmt" "io" "os" ) func main() { file := "D:/gopath/src/golang_development_notes/example/log.txt" f, err := os.Open(file) if err != nil { panic(err) } defer f.Close() chunks := make([]byte, 0) buf := make([]byte, 1024) for { n, err := f.Read(buf) if err != nil && err != io.EOF { panic(err) } if 0 == n { break } chunks = append(chunks, buf[:n]...) } fmt.Println(string(chunks)) }

3. Read by line

package main import ( "bufio" "fmt" "io" "io/ioutil" "os" "strings" ) func main() { filepath := "D:/gopath/src/golang_development_notes/example/log.txt" file, err := os.OpenFile(filepath, os.O_RDWR, 0666) if err != nil { fmt.Println("Open file error!", err) return } defer file.Close() stat, err := file.Stat() if err != nil { panic(err) } var size = stat.Size() fmt.Println("file size=", size) buf := bufio.NewReader(file) for { line, err := buf.ReadString('\n') line = strings.TrimSpace(line) fmt.Println(line) if err != nil { if err == io.EOF { fmt.Println("File read ok!") break } else { fmt.Println("Read file error!", err) return } } } }

write file

There are the following write modes

1,ioutil.WriteFile

package main import ( "io/ioutil" ) func main() { content := []byte("Test 1\n Test 2\n") err := ioutil.WriteFile("test.txt", content, 0644) if err != nil { panic(err) } }

In this way, the test.txt content will be overwritten every time. If the test.txt file does not exist, it will be created.

2,os

package main import ( "fmt" "io" "os" ) func checkFileIsExist(filename string) bool { if _, err := os.Stat(filename); os.IsNotExist(err) { return false } return true } func main() { var wireteString = "Test 1\n Test 2\n" var filename = "./test.txt" var f *os.File var err1 error if checkFileIsExist(filename) { //If the file exists f, err1 = os.OpenFile(filename, os.O_APPEND, 0666) //Open file fmt.Println("File exists") } else { f, err1 = os.Create(filename) //create a file fmt.Println("file does not exist") } defer f.Close() n, err1 := io.WriteString(f, wireteString) //Write file (string) if err1 != nil { panic(err1) } fmt.Printf("Write in %d Byte n", n) }

This method adds new content at the end of the file content.

3,

package main import ( "fmt" "os" ) func checkFileIsExist(filename string) bool { if _, err := os.Stat(filename); os.IsNotExist(err) { return false } return true } func main() { var str = "Test 1\n Test 2\n" var filename = "./test.txt" var f *os.File var err1 error if checkFileIsExist(filename) { //If the file exists f, err1 = os.OpenFile(filename, os.O_APPEND, 0666) //Open file fmt.Println("File exists") } else { f, err1 = os.Create(filename) //create a file fmt.Println("file does not exist") } defer f.Close() n, err1 := f.Write([]byte(str)) //Write file (byte array) fmt.Printf("Write in %d Byte n", n) n, err1 = f.WriteString(str) //Write file (string) if err1 != nil { panic(err1) } fmt.Printf("Write in %d Byte n", n) f.Sync() }

This method adds new content at the end of the file content.

4,bufio

package main import ( "bufio" "fmt" "os" ) func checkFileIsExist(filename string) bool { if _, err := os.Stat(filename); os.IsNotExist(err) { return false } return true } func main() { var str = "Test 1\n Test 2\n" var filename = "./test.txt" var f *os.File var err1 error if checkFileIsExist(filename) { //If the file exists f, err1 = os.OpenFile(filename, os.O_APPEND, 0666) //Open file fmt.Println("File exists") } else { f, err1 = os.Create(filename) //create a file fmt.Println("file does not exist") } defer f.Close() if err1 != nil { panic(err1) } w := bufio.NewWriter(f) //Create a new Writer object n, _ := w.WriteString(str) fmt.Printf("Write in %d Byte n", n) w.Flush() }

This method adds new content at the end of the file content.

Compare the efficiency of several read files

package main import ( "bufio" "fmt" "io" "io/ioutil" "os" "time" ) func read0(path string) string { file, err := os.Open(path) if err != nil { panic(err) } defer file.Close() content, err := ioutil.ReadAll(file) return string(content) } func read1(path string) string { content, err := ioutil.ReadFile(path) if err != nil { panic(err) } return string(content) } func read2(path string) string { fi, err := os.Open(path) if err != nil { panic(err) } defer fi.Close() r := bufio.NewReader(fi) chunks := make([]byte, 0) buf := make([]byte, 1024) //How many bytes are read at a time for { n, err := r.Read(buf) if err != nil && err != io.EOF { panic(err) } if 0 == n { break } chunks = append(chunks, buf[:n]...) } return string(chunks) } func read3(path string) string { fi, err := os.Open(path) if err != nil { panic(err) } defer fi.Close() chunks := make([]byte, 0) buf := make([]byte, 1024) for { n, err := fi.Read(buf) if err != nil && err != io.EOF { panic(err) } if 0 == n { break } chunks = append(chunks, buf[:n]...) } return string(chunks) } func main() { file := "D:/gopath/src/example/example/log.txt" start := time.Now() read0(file) t0 := time.Now() fmt.Printf("Cost time %v\n", t0.Sub(start)) read1(file) t1 := time.Now() fmt.Printf("Cost time %v\n", t1.Sub(t0)) read2(file) t2 := time.Now() fmt.Printf("Cost time %v\n", t2.Sub(t1)) read3(file) t3 := time.Now() fmt.Printf("Cost time %v\n", t3.Sub(t2)) }

Operation result:

For the first time

Cost time 6.0003ms
Cost time 3.0002ms
Cost time 7.0004ms
Cost time 11.0006ms

The second time

Cost time 7.0004ms
Cost time 4.0003ms
Cost time 6.0003ms
Cost time 8.0005ms

Third time

Cost time 9.0006ms
Cost time 3.0001ms
Cost time 7.0004ms
Cost time 11.0007ms

4 December 2019, 09:05 | Views: 4471