package main

import (

    "os"

    "strings"

    "time"

    "fmt"

    "strconv"

)    

//耗时统计函数

func timeCost() func() {

    start := time.Now()

    return func() {

        tc := time.Since(start)

        fmt.Printf("time cost = %v\n", tc)

    }

}

func sum(n int, fd *os.File)  {

    defer timeCost()()        //注意，是对 timeCost()返回的函数进行调用，因此需要加两对小括号

    for i:=1; i <= n; i++ {

        stri := strconv.Itoa(i)

           content := "写入的文件内容" + stri

        fd_time := time.Now().Format("2006-01-02 15:04:05")

        fd_content := strings.Join([]string{"======",fd_time,"=====",content,"\n"},"")

        buf := []byte(fd_content)

          fd.Write(buf)

  }

}

func main() {

    fd , _ := os.OpenFile("xyz2.txt",os.O_RDWR|os.O_CREATE|os.O_APPEND,0644)

    sum(10000,fd)

    fd.Close()

}