golang学习笔记 ----读写文件

使用io/ioutil进行读写文件

ioutil包

其中提到了两个方法： 
func ReadFile

func ReadFile(filename string) ([]byte, error)

ReadFile reads the file named by filename and returns the contents. A successful call returns err == nil, not err == EOF. Because ReadFile reads the whole file, it does not treat an EOF from Read as an error to be reported.

func WriteFile

func WriteFile(filename string, data []byte, perm os.FileMode) error

WriteFile writes data to a file named by filename. If the file does not exist, WriteFile creates it with permissions perm; otherwise WriteFile truncates it before writing

读文件：

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)
}

写文件：

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进行读写文件

os包

首先要注意的就是两个打开文件的方法：

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.

　读文件：

fi, err := os.Open(path)
    if err != nil {
        panic(err)
    }
    defer fi.Close()

func OpenFile 
需要提供文件路径、打开模式、文件权限

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.

　　读文件：

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)
    }
}

　　读方法

package main

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

func check(e error) {
    if e != nil {
        panic(e)
    }
}

func main() {

    f, err := os.Open("foo.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()

}

　　写方法

package main

import (
    "bufio"
    "fmt"
    "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()

}

　　

　几种读取文件方法速度比较

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 := "foo.dat"

    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))

}