这是我参与「第三届青训营 -后端场」笔记创作活动的的第1篇笔记
基础语法
Hello World
package main//入口文件
import (
"fmt"
)//（不是‘{’）导入fmt包：输入字符串，格式化字符串；
func main() {
fmt.Println("hello world")
}
变量
var 变量名 [类型] [=] [初始值]
package main
import (
"fmt"
"math"
)
func main() {
var a = "abcde"
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)
fmt.Println(g)
const s string = "contest" //常量，不必确定类型
const h = 500
const i = 3e10/h
fmt.Println(s,h,i,math.Sin(h),math.Sin(i))
}
if-else条件
与C和C++不同的是if(条件块不用括号),但是必须要加大括号
package main
import (
"fmt"
)
func main() {
if 7%2!=0{
fmt.Println("7 is even")
}else {
fmt.Println("7 is odd")
}
}
循环
只有for循环
package main
import (
"fmt"
)
func main() {
for j :=7; j < 9; j++ {
fmt.Println(j)
}
}
switch语句
switch中不需要加break
package main
import (
"fmt"
)
func main() {
a := 2
switch(a){
case 1:
fmt.Println("one")
case 2:
fmt.Println("two")
case 3:
fmt.Println("three")
default:
fmt.Println("other")
}
}
数组
package main
import (
"fmt"
)
func main() {
var a [5]int
a[4] = 100
fmt.Println(a[4],len(a))
}
切片
数组是固定长度，切片可以更改
append的结果必须赋值为原数组
slice原理是储存了一个长度和容量，加一个指向数组的指针，执行append的过程中，如果容量不够会扩容并返回新的slice
与python不同：不支持负数索引
package main
import (
"fmt"
)
func main() {
s := make([]string,3)
s[0] = "a"
s[1] = "b"
s[2] = "c"
s = append(s,"d")
s = append(s,"e","f")
fmt.Println(s[2:5])
}
map
package main
import (
"fmt"
)
func main() {
m := make(map[string]int)//第一个为key的类型，第二个是value的类型
m["one"] = 1
m["two"] = 2
fmt.Println(m)
fmt.Println(len(m))
//删除
delete(m,"one")
fmt.Println(m)
}
range
遍历slice和map
package main
import (
"fmt"
)
func main() {
nums := []int{2, 3, 4}
sum := 0
for num := range nums {
sum += num
}
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
}
}
函数
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
}
指针
作用：修改参数
package main
import (
"fmt"
)
func add2(n int){
n += 2
}//无效 需写成指针
func add2ptr(n *int) {
*n += 2
}
func main() {
n := 5
fmt.Println(n)//5
add2ptr(&n)
fmt.Println(n) // 7
}
结构体
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
}
结构体方法
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
}//带指针就能修改结构体
func main() {
a := user{name: "wang", password: "1024"}
a.resetPassword("2048")
fmt.Println(a.checkPassword("2048")) // true
}
错误处理
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)
}
}
字符串操作
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 ,(一个中文可能会对应多个字符)
}
字符串格式化
不同于C/C++的printf，go只需用%v打印任意变量,+v会打印详细结果，#v更详细
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处理
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"}}
}
时间处理
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println(now) //打印现在时间2022-05-08 00:58:37.164660204 +0800 CST
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()) // 1651942717
}
数字解析
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
}
进程信息
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
}
