go的相关包time、os、rand、fmt

time

1、time包

2、time.Time类型， 用来表示时间

3、取当前时间， now := time.Now()

4、time.Now().Day()，time.Now().Minute()，time.Now().Month()，time.Now().Year()，

second := now.Unix() //按秒计

5、格式化，fmt.Printf(“%02d/%02d%02d %02d:%02d:%02d”, now.Year()…)

package main

import(
    "time"
    "fmt"
)

func testTime() {
    for {
        now := time.Now()
        fmt.Printf("type of now is:%T
", now)

        year := now.Year()
        month := now.Month()
        day := now.Day()

        str := fmt.Sprintf("%04d-%02d-%02d %02d:%02d:%02d
", year, month, day, now.Hour(), now.Minute(), now.Second())
        fmt.Println(str)        

        fmt.Printf("timestamp:%d
", now.Unix())  //时间戳
    }
}

6、time.Duration 用来表示纳秒 

7、 一些常量量： 

const ( 　　

　　 Nanosecond Duration = 1 

Microsecond= 1000 * Nanosecond //纳秒

Millisecond= 1000 * Microsecond //微妙

Second= 1000 * Millisecond //毫秒

Minute= 60 * Second 

Hour= 60 * Minute

) 

package main

import(
    "time"
    "fmt"
)

func testTimeConst() {
    fmt.Printf("Nanosecond :%d
", time.Nanosecond)  //1
    fmt.Printf("Microsecond:%d
", time.Microsecond)  //1000
    fmt.Printf("Millisecond:%d
", time.Millisecond)      //1000000
    fmt.Printf("second     :%d
", time.Second)
    fmt.Printf("Minute     :%d
", time.Minute)
    fmt.Printf("Hour       :%d
", time.Hour)
}

8. 格式化： 

now := time.Now() 

fmt.Println(now.Format(“02/1/2006 15:04:05”))    //02/1/2006 03:04:05   十二小时制

fmt.Println(now.Format(“2006/1/02 15:04:05”)) 

fmt.Println(now.Format(“2006/1/02”))

package main

import(
    "time"
    "fmt"
)
func main() {
    now := time.Now()
    str := now.Format("2006-01-02 03:04:05")
    fmt.Printf("format result:%s
", str)
}

练习：写 一个程序，统计一段代码的执行耗时，单位精确到微秒 

package main

import(
    "time"
    "fmt"
)

func main() {
    start := time.Now().UnixNano()  //纳秒为单位
    /*
    业务代码
    */
    time.Sleep(10*time.Millisecond)
    end := time.Now().UnixNano()
    cost := (end - start)/1000
    fmt.Printf("cost:%dus
", cost)
}

  

os 

package main
import (
     "fmt"
     "os" 
) 

func main() {   
      var goos string = os.Getenv("OS")      //操作系统的名字
      fmt.Printf("The operating system is: %s
", goos) 
      path := os.Getenv("PATH")                 //GOPATH的路径   
      fmt.Printf("Path is %s
", path) 
} 

math/rand

fmt   

各种方法集合：

格式化输出：

package main
import "fmt"
func main() {
   var a int = 100
   var b bool
   c := 'a'

   fmt.Printf("%+v
", a)   //类似%v，但输出结构体时会添加字段名
   fmt.Printf("%#v
", b)  //相应值的Go语法表示
   fmt.Printf("%T
", c)    //值的类型的Go语法表示
   fmt.Printf("90%%
")   //字面上的%
   fmt.Printf("%t
", b)  //布尔值
   fmt.Printf("%b
", 100) //二进制
   fmt.Printf("%f
", 199.22)  //浮点型，有小数点，但没有指数
   fmt.Printf("%q
", "this is a test")  //双引号围绕的字符字面值
   fmt.Printf("%x
", 39839333)   //每个字节用两字符十六进制数表示（使用a-f）
   fmt.Printf("%p
", &a)   //传入指针，表示为十六进制，并加上前导的0x
   fmt.Printf("%c
", 87)   //相应Unicode码所表示的字符
   
   str := fmt.Sprintf("a=%d", a)  // 将a转化为字符串
   fmt.Printf("%q
", str)
}

 格式化输入：

package main

import "fmt"

var number int
var str string

func main() {
   fmt.Scanf("%d", &number)
   fmt.Scanf("%s", &str)
   fmt.Println(number, str)
}