Golang基础-字节跳动青训营

Golang

安装

1. 访问 https://go.dev/ ，点击 Download ，下载对应平台安装包，安装即可
2. 如果无法访问上述网址，可以改为访问 https://studygolang.com/dl 下载安装
3. 如果访问 github 速度比较慢，建议配置 go mod proxy，参考 https://goproxy.cn/ 里面的描述配置，下载第三方依赖包的速度可以大大加快

示例代码

1. Windows 平台建议安装 git，其它系统自带，安装教程
2. 打开 https://github.com/wangkechun/go-by-example 克隆课程示例项目
3. 进入课程示例项目代码目录，运行 go run example/01-hello/main.go 如果正确输出 hello world，则说明环境配置正确

var

package main

import (
	"fmt"
	"math"
)

func main() {
	// 自动推导类型
	var a = "initial"
	// 定义多个变量
	var b, c int = 1, 2
	var d = true
	var e float64
	f := float32(e)
	g := a + "foo"
	fmt.Println(a, b, c, d, e, f) // initial 1 2 true 0 0
	fmt.Println(g)                // initialapple
	const s string = "constant"
	const h = 500000000
	const i = 3e20 / h
	fmt.Println(s, h, i, math.Sin(h), math.Sin(i))
}

for

package main

import "fmt"

func main() {
	i := 1
	for {
		fmt.Println("loop")
		break
	}
	for j := 7; j < 9; j++ {
		fmt.Println(j)
	}

	for n := 0; n < 5; n++ {
		if n%2 == 0 {
			continue
		}
		fmt.Println(n)
	}
	for i <= 3 {
		fmt.Println(i)
		i = i + 1
	}
}

if

package main

import "fmt"

func main() {
	if 7%2 == 0 {
		fmt.Println("7 is even")
	} else {
		fmt.Println("7 is odd")
	}

	if 8%4 == 0 {
		fmt.Println("8 is divisible by 4")
	}

	if num := 9; num < 0 {
		fmt.Println(num, "is negative")
	} else if num < 10 {
		fmt.Println(num, "has 1 digit")
	} else {
		fmt.Println(num, "has multiple digits")
	}
}

switch

package main

import (
	"fmt"
	"time"
)

func main() {
	a := 2
	switch a {
	case 1:
		fmt.Println("one")
	case 2:
		fmt.Println("two")
	case 3:
		fmt.Println("three")
	case 4, 5:
		fmt.Println("four or five")
	default:
		fmt.Println("other")
	}

	t := time.Now()
	switch {
	case t.Hour() < 12:
		fmt.Println("It's before noon")
	default:
		fmt.Println("It's after noon")
	}
}

array

package main

import "fmt"

func main() {
	var a [5]int
	a[4] = 100
	fmt.Println("get:", a[2])
	fmt.Println("len:", len(a))

	b := [5]int{1, 2, 3, 4, 5}
	fmt.Println(b)

	var twoD [2][3]int
	for i := 0; i < 2; i++ {
		for j := 0; j < 3; j++ {
			twoD[i][j] = i + j
		}
	}
	fmt.Println("2d: ", twoD)
}

slice

package main

import "fmt"

func main() {

	s := make([]string, 3)
	s[0] = "a"
	s[1] = "b"
	s[2] = "c"
	fmt.Println("get:", s[2])   // c
	fmt.Println("len:", len(s)) // 3

	s = append(s, "d")
	s = append(s, "e", "f")
	fmt.Println(s) // [a b c d e f]

	c := make([]string, len(s))
	copy(c, s)
	fmt.Println(c) // [a b c d e f]

	fmt.Println(s[2:5]) // [c d e]
	fmt.Println(s[:5])  // [a b c d e]
	fmt.Println(s[2:])  // [c d e f]

	good := []string{"g", "o", "o", "d"}
	fmt.Println(good) // [g o o d]
}

map

package main

import "fmt"

func main() {
	m := make(map[string]int)
	m["one"] = 1
	m["two"] = 2
	fmt.Println(m)           // map[one:1 two:2]
	fmt.Println(len(m))      // 2
	fmt.Println(m["one"])    // 1
	fmt.Println(m["unknow"]) // 0

	r, ok := m["unknow"]
	fmt.Println(r, ok) // 0 false

	delete(m, "one")

	m2 := map[string]int{"one": 1, "two": 2}
	var m3 = map[string]int{"one": 1, "two": 2}
	fmt.Println(m2, m3)
}

range

package main

import "fmt"

func main() {
	nums := []int{2, 3, 4}
	sum := 0
	for i, num := range nums {
		sum += num
		if num == 2 {
			fmt.Println("index:", i, "num:", num) // index: 0 num: 2
		}
	}
	fmt.Println(sum) // 9

	m := map[string]string{"a": "A", "b": "B"}
	for k, v := range m {
		fmt.Println(k, v) // b 8; a A
	}
	for k := range m {
		fmt.Println("key", k) // key a; key b
	}
}

func

package main

import "fmt"

func add(a int, b int) int {
	return a + b
}

func add2(a, b int) int {
	return a + b
}

func exists(m map[string]string, k string) (v string, ok bool) {
	v, ok = m[k]
	return v, ok
}

func main() {
	res := add(1, 2)
	fmt.Println(res) // 3

	v, ok := exists(map[string]string{"a": "A"}, "a")
	fmt.Println(v, ok) // A True
}

point

package main

import "fmt"

func add2(n int) {
	n += 2
}

func add2ptr(n *int) {
	*n += 2
}

func main() {
	n := 5
	add2(n)
	fmt.Println(n) // 5
	add2ptr(&n)
	fmt.Println(n) // 7
}

struct

package main

import "fmt"

type user struct {
	name     string
	password string
}

func main() {
	a := user{name: "wang", password: "1024"}
	b := user{"wang", "1024"}
	c := user{name: "wang"}
	c.password = "1024"
	var d user
	d.name = "wang"
	d.password = "1024"

	fmt.Println(a, b, c, d)                 // {wang 1024} {wang 1024} {wang 1024} {wang 1024}
	fmt.Println(checkPassword(a, "haha"))   // false
	fmt.Println(checkPassword2(&a, "haha")) // false
}

func checkPassword(u user, password string) bool {
	return u.password == password
}

func checkPassword2(u *user, password string) bool {
	return u.password == password
}

struct-method

package main

import "fmt"

type user struct {
	name     string
	password string
}

func (u user) checkPassword(password string) bool {
	return u.password == password
}

func (u *user) resetPassword(password string) {
	u.password = password
}

func main() {
	a := user{name: "wang", password: "1024"}
	a.resetPassword("2048")
	fmt.Println(a.checkPassword("2048")) // true
}

error

package main

import (
	"errors"
	"fmt"
)

type user struct {
	name     string
	password string
}

func findUser(users []user, name string) (v *user, err error) {
	for _, u := range users {
		if u.name == name {
			return &u, nil
		}
	}
	return nil, errors.New("not found")
}

func main() {
	u, err := findUser([]user{{"wang", "1024"}}, "wang")
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Println(u.name) // wang

	if u, err := findUser([]user{{"wang", "1024"}}, "li"); err != nil {
		fmt.Println(err) // not found
		return
	} else {
		fmt.Println(u.name)
	}
}

string

package main

import (
	"fmt"
	"strings"
)

func main() {
	a := "hello"
	fmt.Println(strings.Contains(a, "ll"))                // true
	fmt.Println(strings.Count(a, "l"))                    // 2
	fmt.Println(strings.HasPrefix(a, "he"))               // true
	fmt.Println(strings.HasSuffix(a, "llo"))              // true
	fmt.Println(strings.Index(a, "ll"))                   // 2
	fmt.Println(strings.Join([]string{"he", "llo"}, "-")) // he-llo
	fmt.Println(strings.Repeat(a, 2))                     // hellohello
	fmt.Println(strings.Replace(a, "e", "E", -1))         // hEllo
	fmt.Println(strings.Split("a-b-c", "-"))              // [a b c]
	fmt.Println(strings.ToLower(a))                       // hello
	fmt.Println(strings.ToUpper(a))                       // HELLO
	fmt.Println(len(a))                                   // 5
	b := "你好"
	fmt.Println(len(b)) // 6
}

fmt

package main

import "fmt"

type point struct {
	x, y int
}

func main() {
	s := "hello"
	n := 123
	p := point{1, 2}
	fmt.Println(s, n) // hello 123
	fmt.Println(p)    // {1 2}

	fmt.Printf("s=%v\n", s)  // s=hello
	fmt.Printf("n=%v\n", n)  // n=123
	fmt.Printf("p=%v\n", p)  // p={1 2}
	fmt.Printf("p=%+v\n", p) // p={x:1 y:2}
	fmt.Printf("p=%#v\n", p) // p=main.point{x:1, y:2}

	f := 3.141592653
	fmt.Println(f)          // 3.141592653
	fmt.Printf("%.2f\n", f) // 3.14
}

json

package main

import (
	"encoding/json"
	"fmt"
)

type userInfo struct {
	Name  string
	Age   int `json:"age"`
	Hobby []string
}

func main() {
	a := userInfo{Name: "wang", Age: 18, Hobby: []string{"Golang", "TypeScript"}}
	buf, err := json.Marshal(a)
	if err != nil {
		panic(err)
	}
	fmt.Println(buf)         // [123 34 78 97...]
	fmt.Println(string(buf)) // {"Name":"wang","age":18,"Hobby":["Golang","TypeScript"]}

	buf, err = json.MarshalIndent(a, "", "\t")
	if err != nil {
		panic(err)
	}
	fmt.Println(string(buf))

	var b userInfo
	err = json.Unmarshal(buf, &b)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%#v\n", b) // main.userInfo{Name:"wang", Age:18, Hobby:[]string{"Golang", "TypeScript"}}
}

time

package main

import (
	"fmt"
	"time"
)

func main() {
	now := time.Now()
	fmt.Println(now) // 2022-03-27 18:04:59.433297 +0800 CST m=+0.000087933
	t := time.Date(2022, 3, 27, 1, 25, 36, 0, time.UTC)
	t2 := time.Date(2022, 3, 27, 2, 30, 36, 0, time.UTC)
	fmt.Println(t)                                                  // 2022-03-27 01:25:36 +0000 UTC
	fmt.Println(t.Year(), t.Month(), t.Day(), t.Hour(), t.Minute()) // 2022 March 27 1 25
	fmt.Println(t.Format("2006-01-02 15:04:05"))                    // 2022-03-27 01:25:36
	diff := t2.Sub(t)
	fmt.Println(diff)                           // 1h5m0s
	fmt.Println(diff.Minutes(), diff.Seconds()) // 65 3900
	t3, err := time.Parse("2006-01-02 15:04:05", "2022-03-27 01:25:36")
	if err != nil {
		panic(err)
	}
	fmt.Println(t3 == t)    // true
	fmt.Println(now.Unix()) // 1648738080
}

strconv

package main

import (
	"fmt"
	"strconv"
)

func main() {
	f, _ := strconv.ParseFloat("1.234", 64)
	fmt.Println(f) // 1.234

	n, _ := strconv.ParseInt("111", 10, 64)
	fmt.Println(n) // 111

	n, _ = strconv.ParseInt("0x1000", 0, 64)
	fmt.Println(n) // 4096

	n2, _ := strconv.Atoi("123")
	fmt.Println(n2) // 123

	n2, err := strconv.Atoi("AAA")
	fmt.Println(n2, err) // 0 strconv.Atoi: parsing "AAA": invalid syntax
}

env

package main

import (
	"fmt"
	"os"
	"os/exec"
)

func main() {
	// go run example/20-env/main.go a b c d
	fmt.Println(os.Args)           // [/var/folders/8p/n34xxfnx38dg8bv_x8l62t_m0000gn/T/go-build3406981276/b001/exe/main a b c d]
	fmt.Println(os.Getenv("PATH")) // /usr/local/go/bin...
	fmt.Println(os.Setenv("AA", "BB"))

	buf, err := exec.Command("grep", "127.0.0.1", "/etc/hosts").CombinedOutput()
	if err != nil {
		panic(err)
	}
	fmt.Println(string(buf)) // 127.0.0.1       localhost
}

Curl转Go

https://curlconverter.com/#go

Json转Struct

https://oktools.net/json2go