讀文件：
package main import ( "fmt" "io/ioutil" ) func main() { b, err := ioutil.ReadFile("test.log") if err != nil { fmt.Print(err) } fmt.Println(b) str := string(b) fmt.Println(str) }寫文件：
package main import ( "io/ioutil" ) func check(e error) { if e != nil { panic(e) } } func main() { d1 := []byte("hello\ngo\n") err := ioutil.WriteFile("test.txt", d1, 0644) check(err) }使用os進行讀寫文件
同樣，先回憶下之前的os包的介紹：
Go語言學習之os包中文件相關的操作(The way to go)
首先要注意的就是兩個打開文件的方法：
func Open
func Open(name string) (*File, error)
Open opens the named file for reading. If successful, methods on the returned file can be used for reading; the associated file descriptor has mode O_RDONLY. If there is an error, it will be of type *PathError.
讀文件：
fi, err := os.Open(path)
if err != nil { panic(err) } defer fi.Close()func OpenFile
需要提供文件路徑、打開模式、文件權限
func OpenFile(name string, flag int, perm FileMode) (*File, error)OpenFile is the generalized open call; most users will use Open or Create instead. It opens the named file with specified flag (O_RDONLY etc.) and perm, (0666 etc.) if applicable. If successful, methods on the returned File can be used for I/O. If there is an error, it will be of type *PathError.
讀文件：
package main import ( "log" "os" ) func main() { f, err := os.OpenFile("notes.txt", os.O_RDWR|os.O_CREATE, 0755) if err != nil { log.Fatal(err) } if err := f.Close(); err != nil { log.Fatal(err) } }
讀方法
package main import ( "bufio" "fmt" "io" "io/ioutil" "os" ) func check(e error) { if e != nil { panic(e) } } func main() { f, err := os.Open("/tmp/dat") check(err) b1 := make([]byte, 5) n1, err := f.Read(b1) check(err) fmt.Printf("%d bytes: %s\n", n1, string(b1)) o2, err := f.Seek(6, 0) check(err) b2 := make([]byte, 2) n2, err := f.Read(b2) check(err) fmt.Printf("%d bytes @ %d: %s\n", n2, o2, string(b2)) o3, err := f.Seek(6, 0) check(err) b3 := make([]byte, 2) n3, err := io.ReadAtLeast(f, b3, 2) check(err) fmt.Printf("%d bytes @ %d: %s\n", n3, o3, string(b3)) _, err = f.Seek(0, 0) check(err) r4 := bufio.NewReader(f) b4, err := r4.Peek(5) check(err) fmt.Printf("5 bytes: %s\n", string(b4)) f.Close() }
寫方法
package main import ( "bufio" "fmt" "io/ioutil" "os" ) func check(e error) { if e != nil { panic(e) } } func main() { f, err := os.Create("/tmp/dat2") check(err) defer f.Close() d2 := []byte{115, 111, 109, 101, 10} n2, err := f.Write(d2) check(err) fmt.Printf("wrote %d bytes\n", n2) n3, err := f.WriteString("writes\n") fmt.Printf("wrote %d bytes\n", n3) f.Sync() w := bufio.NewWriter(f) n4, err := w.WriteString("buffered\n") fmt.Printf("wrote %d bytes\n", n4) w.Flush() }
幾種讀取文件方法速度比較
package main import ( "bufio" "fmt" "io" "io/ioutil" "os" "time" ) func read0(path string) string { f, err := ioutil.ReadFile(path) if err != nil { fmt.Printf("%s\n", err) panic(err) } return string(f) } func read1(path string) string { fi, err := os.Open(path) if err != nil { panic(err) } defer fi.Close() chunks := make([]byte, 1024, 1024) 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 read2(path string) string { fi, err := os.Open(path) if err != nil { panic(err) } defer fi.Close() r := bufio.NewReader(fi) chunks := make([]byte, 1024, 1024) buf := make([]byte, 1024) 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() fd, err := ioutil.ReadAll(fi) return string(fd) } func main() { file := "test.log" 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)) }
運行結果：
Cost time 4.0105ms
Cost time 11.5043ms
Cost time 7.0042ms
Cost time 2.4983ms
Cost time 4.4925ms
Cost time 11.0053ms
Cost time 5.0082ms
Cost time 2.9992ms
Cost time 3.9866ms
Cost time 15.0085ms
Cost time 7.5054ms
Cost time 2.5035ms
Cost time 4.9989ms
Cost time 14.0112ms
Cost time 7.5045ms
Cost time 3.508ms
Cost time 3.0043ms
Cost time 15.0265ms
Cost time 8.9884ms
Cost time 2.0036ms