# iota和<<左移>>右移的用法

2018/01/23 23:03

在go语言中iota比较特殊，是一个被编译器修改的常量，在每一个const关键字出现时被重置为0，然后在下一个const出现之前，每出现一次iota，其所代表的数字就会自动加1

左移运算符”<<”是双目运算符。左移n位就是乘以2的n次方。 其功能把”<<”左边的运算数的各二进位全部左移若干位，由”<<”右边的数指定移动的位数，高位丢弃，低位补0。

右移运算符”>>”是双目运算符。右移n位就是除以2的n次方。 其功能是把”>>”左边的运算数的各二进位全部右移若干位，”>>”右边的数指定移动的位数。

package iota

import "fmt"

func Test()  {

const(
c1 = iota  //c1=0
c2 = iota  //c2=1
c3 = iota  //c3=2
)

fmt.Println("c1 = ",c1," c2 = ",c2," c3 = ",c3,"\n")

const(
a = 1 << iota //a = 1
b = 1 << iota //b = 2
c = 1 << iota //c = 4
)
fmt.Println("a = ",a," b = ",b," c = ",c,"\n")

const(
v1 = iota //v1 = 0
v2        //v2 = 1
v3        //v3 = 2
)
fmt.Println("v1 = ",v1," v2 = ",v2," v3 = ",v3,"\n")

const(
x = 1 <<iota //x = 1
y             //y = 2
z             //z = 4
)
fmt.Println("x = ",x," y = ",y," z = ",z)
}

package main

import (
"fmt"
)

func main() {
const (
a2 = 1 << iota   //iota = 0  a2 = 1 X 2的0次方
b2 = 3 << iota   //iota = 1  b2 = 3 X 2的1次方
c2               //iota = 2  c2 = 3 X 2的2次方
d2               //iota = 3  d2 = 3 X 2的3次方
e2 = 120 >> iota //iota = 4  e2 = 120 / 2的4次方
f2               //iota = 5  f2 = 120 / 2的5次方
)

fmt.Println(a2, b2, c2, d2, e2, f2)
//1 6 12 24 7 3
}


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