Golang 汇总

Desc: 所有的关于go的学习问题记录都在这个文章

安装部分

问题一: 安装后command not found

sh-3.2# go -version 
sh: go: command not found

• 问题一解决方案:

1. check config file:

   vim ~/.bash_profile

• 如果没有bash_profile就创建

2. 写入:

   export GOROOT=/usr/local/go
   export GOPATH=/usr/local/GO
   #GOPATH可以写自己项目的文件地址
   export PATH=$PATH:$GOROOT/bin:$GOPATH/bin

3. 保存后:

   source ~/.bash_profile

4. check if it works.

   sh-3.2# go version 
   go version go1.18 darwin/amd64

学习部分

const关键字&& iota表达式

• go 变量声明 ：关键字 + 变量名 + 变量类型

package main

import "fmt"

const (
  //iota是一个 表达式
  BEIJING = 10 * iota //iota = 0
  SHNAGHAI, // iota == 1
  SHENZHEN, // iota == 2
)
const (
  //批量赋值
	a,b = iota + 1 , iota + 2 // iota = 0 
  c,d // iota = 1
  e,f
  
  g,h = iota * 2 , iota * 3
  i,k
  l,m
)

func main(){
  const length int = 123 
  fmt.Println("beijing = ", BEIJING)
	fmt.Println("shanghai = ", SHANGHAI)
	fmt.Println("shenzhen = ", SHENZHEN)

	fmt.Println("ab cd ef = ", a, b, c, d, e, f)
	fmt.Println("gh ik lm = ", g, h, i, k, l, m)
}

beijing =  0
shanghai =  10
shenzhen =  20
ab cd ef =  1 2 2 3 3 4
gh ik lm =  6 9 8 12 10 15

GO方法声明和返回值

• 关键字 + 方法名 + 返回值类型

eg : func test(args .. ) int

package main

import "fmt"

func test(a string, b int) int {
	fmt.Println("a ", a)
	fmt.Println("b ", b)
	c := 11
	return c
}

//返回多个返回值 匿名形参
func test1(a string, b int) (int, int) {
	fmt.Println("method name =", a)
	fmt.Println("arg int =", b)
	return 22, 33
}

//返回多个返回值 有形参名称
//或者可以写 func test2(a string, b int) (r1 , r2 int)
func test2(a string, b int) (r1 int, r2 int) {
	fmt.Println("method name =", a)
	fmt.Println("arg int =", b)
	fmt.Println("r1 = ", r1)
	fmt.Println("r2 = ", r2)
	// 返回值赋值
	r1 = 44
	r2 = 55
	return
}
func main() {
	c := test("123", 512)
	fmt.Println("c= ", c)

	ret1, ret2 := test1("test1", 1024)
	fmt.Println("ret1 , ret2 :", ret1, ret2)

	ret3, ret4 := test2("test2", 2048)
	fmt.Println("ret3 , ret4 :", ret3, ret4)
}

a  123
b  512
c=  11
method name = test1
arg int = 1024
ret1 , ret2 : 22 33
method name = test2
arg int = 2048
r1 =  0
r2 =  0
ret3 , ret4 : 44 55

go指针

demo：

var (
	tmp *int 
  q *int
  p *int
) //batch 声明

	var a int = 10
	var b int = 20
	//指针赋值
	p = &a
	q = &b

	fmt.Println("p , q", *p, *q)
	//简单指针操作：交换
	tmp = p
	p = q
	q = tmp

	fmt.Println("p , q", *p, *q)
	//二级指针
  var (
    dd **int
  )
	var qq *int
	qq = &a
	dd = &qq

	fmt.Println("qq:", *qq)
	fmt.Println("dd:", **dd)

输出：

p , q 10 20
p , q 20 10
qq: 10
dd: 10

defer 关键字

• return和defer 的优先级 demo：

package main

import "fmt"

func f1() {
	fmt.Println("f1")
}
func f2() {
	fmt.Println("f2")
}
func f3() {
	fmt.Println("f3")
}

func Who_Is_First_Test() int {
  defer defer_call()
  return return_call()
}

func defer_call() int {
  fmt.Println("defer func call")
	return 0
}
func return_call() int {
  fmt.Println("defer func call")
	return 0
}

func mian(){
  defer fmt.Println("main end1")
  defer fmt.Println("main end2)
	
	defer f1()
	defer f2()
	defer f3()

	fmt.Println("main body output1 ")
	fmt.Println("main body output2 ")
	fmt.Println("whos is first ?" , Who_Is_First_Test())

}

main body output1 
main body output2 
return func call
defer func call
Who is first? 1
f3
f2
f1
main end2
main end1