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  • 使用io/ioutil进行读写文件

    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
    go
    ")
        err := ioutil.WriteFile("test.txt", d1, 0644)
        check(err)
    }

    使用os进行读写文件

    同样,先回忆下之前的os包的介绍: 
    Go语言学习之os包中文件相关的操作(The way to go)

    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
    ", 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
    ", 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
    ", 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
    ", 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
    ", n2)
    
        n3, err := f.WriteString("writes
    ")
        fmt.Printf("wrote %d bytes
    ", n3)
    
    
        f.Sync()
    
    
        w := bufio.NewWriter(f)
        n4, err := w.WriteString("buffered
    ")
        fmt.Printf("wrote %d bytes
    ", 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
    ", 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
    ", t0.Sub(start))
    
        read1(file)
        t1 := time.Now()
        fmt.Printf("Cost time %v
    ", t1.Sub(t0))
    
        read2(file)
        t2 := time.Now()
        fmt.Printf("Cost time %v
    ", t2.Sub(t1))
    
        read3(file)
        t3 := time.Now()
        fmt.Printf("Cost time %v
    ", 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

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  • 原文地址:https://www.cnblogs.com/craneboos/p/9071662.html
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