Go语言-读写文件

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摘要

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Go读写文件的一些包的使用方法

io/ioutil

主要是操作文件、文件夹

ReadAll

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func ReadAll(r io.Reader) ([]byte, error)
  • 读取r中的所有数据，返回读取的数据和遇到的错误
  • 如果读取成功，则err返回nil，而不是EOF，因为ReadAll定义为读取所有数据，所以不会把EOF当做错误处理。
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package main

import (
    "crypto/tls"
    "fmt"
    "io/ioutil"
    "net/http"
)

func main() {

    link := "http://xkcd.com/55"

    tr := &http.Transport{
        TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
    }
    client := &http.Client{Transport: tr}
    response, err := client.Get(link)
    if err != nil {
        fmt.Println(err)
    }
    defer response.Body.Close()

    //block forever at the next line
    content, _ := ioutil.ReadAll(response.Body)

    fmt.Println(string(content))

}

ReadDir

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func ReadDir(dirname string) ([]os.FileInfo, error)
  • ReadDir读取指定目录中的所有目录和文件（不包括子目录）
  • 返回读取到的文件信息列表和遇到的错误，列表是经过排序的。
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package main

import (
    "fmt"
    "io/ioutil"
    "log"
)

func main() {

    files, err := ioutil.ReadDir(".")
    if err != nil {
        log.Fatal(err)
    }

    for _, file := range files {
        fmt.Println(file.Name())
    }

}

ReadFile

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func ReadFile(filename string) ([]byte, error)
  • ReadFile读取文件中的所有数据，返回读取的数据和遇到的错误
  • 如果读取成功，则err返回nil，而不是EOF
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package main

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

// Reading files requires checking most calls for errors.
// This helper will streamline our error checks below.
func check(e error) {
    if e != nil {
        panic(e)
    }
}

func main() {

    // Perhaps the most basic file reading task is
    // slurping a file's entire contents into memory.
    dat, err := ioutil.ReadFile("test.txt")
    check(err)
    fmt.Print(string(dat))

    // You'll often want more control over how and what
    // parts of a file are read. For these tasks, start
    // by `Open`ing a file to obtain an `os.File` value.
    f, err := os.Open("test.txt")
    check(err)

    // Read some bytes from the beginning of the file.
    // Allow up to 5 to be read but also note how many
    // actually were read.
    b1 := make([]byte, 5)
    n1, err := f.Read(b1)
    check(err)
    fmt.Printf("%d bytes: %s\n", n1, string(b1))

    // You can also `Seek` to a known location in the file
    // and `Read` from there.
    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))

    // The `io` package provides some functions that may
    // be helpful for file reading. For example, reads
    // like the ones above can be more robustly
    // implemented with `ReadAtLeast`.
    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))

    // There is no built-in rewind, but `Seek(0, 0)`
    // accomplishes this.
    _, err = f.Seek(0, 0)
    check(err)

    // The `bufio` package implements a buffered
    // reader that may be useful both for its efficiency
    // with many small reads and because of the additional
    // reading methods it provides.
    r4 := bufio.NewReader(f)
    b4, err := r4.Peek(5)
    check(err)
    fmt.Printf("5 bytes: %s\n", string(b4))

    // Close the file when you're done (usually this would
    // be scheduled immediately after `Open`ing with
    // `defer`).
    f.Close()

}

TempDir

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func TempDir(dir, prefix string) (name string, err error)
  • 操作系统中一般都会提供临时目录
  • 比如linux下的/tmp目录（通过os.TempDir()可以获取到)
  • 有时候，我们自己需要创建临时目录，比如Go工具链源码中（src/cmd/go/build.go）
  • 通过TempDir创建一个临时目录，用于存放编译过程的临时文件
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package main

import (
    "io/ioutil"
    "log"
    "os"
    "path/filepath"
)

func main() {
    content := []byte("temporary file's content")
    dir, err := ioutil.TempDir("", "example")
    if err != nil {
        log.Fatal(err)
    }

    defer os.RemoveAll(dir) // clean up

    tmpfn := filepath.Join(dir, "tmpfile")
    if err := ioutil.WriteFile(tmpfn, content, 0666); err != nil {
        log.Fatal(err)
    }
}

TempFile

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func TempFile(dir, prefix string) (f *os.File, err error)
  • TempFile在dir目录中创建一个以prefix为前缀的临时文件，并将其以读写模式打开。返回创建的文件对象和遇到的错误
  • 如果dir为空，则在默认的临时目录中创建文件（参见os.TempDir
  • 多次调用会创建不同的临时文件，调用者可以通过f.Name()获取文件的完整路径
  • 调用本函数所创建的临时文件，应该由调用者自己删除。
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package main

import (
    "io/ioutil"
    "log"
    "os"
)

func main() {
    content := []byte("temporary file's content")
    tmpfile, err := ioutil.TempFile("", "example")
    if err != nil {
        log.Fatal(err)
    }

    defer os.Remove(tmpfile.Name()) // clean up

    if _, err := tmpfile.Write(content); err != nil {
        log.Fatal(err)
    }
    if err := tmpfile.Close(); err != nil {
        log.Fatal(err)
    }
}

WriteFile

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func WriteFile(filename string, data []byte, perm os.FileMode) error
  • WriteFile向文件中写入数据，写入前会清空文件
  • 如果文件不存在，则会以指定的权限创建该文件
  • 返回遇到的错误
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package main

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

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

func main() {

    // To start, here's how to dump a string (or just
    // bytes) into a file.
    d1 := []byte("hello\ngo\n")
    err := ioutil.WriteFile("/tmp/dat1", d1, 0644)
    check(err)

    // For more granular writes, open a file for writing.
    f, err := os.Create("/tmp/dat2")
    check(err)

    // It's idiomatic to defer a `Close` immediately
    // after opening a file.
    defer f.Close()

    // You can `Write` byte slices as you'd expect.
    d2 := []byte{115, 111, 109, 101, 10}
    n2, err := f.Write(d2)
    check(err)
    fmt.Printf("wrote %d bytes\n", n2)

    // A `WriteString` is also available.
    n3, err := f.WriteString("writes\n")
    fmt.Printf("wrote %d bytes\n", n3)

    // Issue a `Sync` to flush writes to stable storage.
    f.Sync()

    // `bufio` provides buffered writers in addition
    // to the buffered readers we saw earlier.
    w := bufio.NewWriter(f)
    n4, err := w.WriteString("buffered\n")
    fmt.Printf("wrote %d bytes\n", n4)

    // Use `Flush` to ensure all buffered operations have
    // been applied to the underlying writer.
    w.Flush()

}

读

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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

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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)
}

os

读

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package main

import (
    "log"
    "os"
)

func main() {
    //需要提供文件路径、打开模式、文件权限
    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

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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

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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))

}

实例

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package main;
 
import (
    "os"
    "fmt"
    "strconv"
)
 
func main() {
 
    //打开文件，返回文件指针
    file, error := os.Open("./1.txt");
    if error != nil {
        fmt.Println(error);
    }
    fmt.Println(file);
    file.Close();
 
    //以读写方式打开文件，如果不存在，则创建
    file2, error := os.OpenFile("./2.txt", os.O_RDWR|os.O_CREATE, 0766);
    if error != nil {
        fmt.Println(error);
    }
    fmt.Println(file2);
    file2.Close();
 
    //创建文件
    //Create函数也是调用的OpenFile
    file3, error := os.Create("./3.txt");
    if error != nil {
        fmt.Println(error);
    }
    fmt.Println(file3);
    file3.Close();
 
    //读取文件内容
    file4, error := os.Open("./1.txt");
    if error != nil {
        fmt.Println(error);
    }
    //创建byte的slice用于接收文件读取数据
    buf := make([]byte, 1024);
    //循环读取
    for {
        //Read函数会改变文件当前偏移量
        len, _ := file4.Read(buf);
 
        //读取字节数为0时跳出循环
        if len == 0 {
            break;
        }
 
        fmt.Println(string(buf));
    }
    file4.Close();
 
    //读取文件内容
    file5, error := os.Open("./1.txt");
    if error != nil {
        fmt.Println(error);
    }
    buf2 := make([]byte, 1024);
    ix := 0;
    for {
        //ReadAt从指定的偏移量开始读取，不会改变文件偏移量
        len, _ := file5.ReadAt(buf2, int64(ix));
        ix = ix + len;
        if len == 0 {
            break;
        }
 
        fmt.Println(string(buf2));
    }
    file5.Close();
 
    //写入文件
    file6, error := os.Create("./4.txt");
    if error != nil {
        fmt.Println(error);
    }
    data := "我是数据\r\n";
    for i := 0; i < 10; i++ {
        //写入byte的slice数据
        file6.Write([]byte(data));
        //写入字符串
        file6.WriteString(data);
    }
    file6.Close();
 
    //写入文件
    file7, error := os.Create("./5.txt");
    if error != nil {
        fmt.Println(error);
    }
    for i := 0; i < 10; i++ {
        //按指定偏移量写入数据
        ix := i * 64;
        file7.WriteAt([]byte("我是数据"+strconv.Itoa(i)+"\r\n"), int64(ix));
    }
    file7.Close();
 
    //删除文件
    del := os.Remove("./1.txt");
    if del != nil {
        fmt.Println(del);
    }
 
    //删除指定path下的所有文件
    delDir := os.RemoveAll("./dir");
    if delDir != nil {
        fmt.Println(delDir);
    }
}