Go实战--golang中读写文件的几种方式

生命不止，继续 go go go !!!

读写文件应该是在开发过程中经常遇到的，今天要跟大家一起分享的就是在golang的世界中，如何读写文件。

使用io/ioutil进行读写文件

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

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"
    "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()

}

写方法

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()

}

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 := "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))

}

运行结果：

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