Hello World

package mainimport ("fmt"
)func main() {fmt.Println("Hello World")
}

变量&常量定义

仅定义不使用会报错 a declared but not used
golang仅定义变量而未赋值的话，则初始值为假，（int为0，bool为false，string为‘'）

package mainimport ("fmt""math"
)func main() {//定义变量//仅定义不使用会报错  a declared but not usedvar a = "initial"var b, c int = 1, 2var d = true//golang仅定义变量而未赋值的话，则初始值为假，（int为0，bool为false，string为‘'）var e float64f := float32(e)g := a + "foo"fmt.Println(a, b, c, d, e, f) //initial 1 2 true 0 0fmt.Println(g)                //initialfoo//定义常量const s string = "constant"const h = 500000const i = 3e20 / hfmt.Println(s, h, i, math.Sin(h), math.Sin(i))
}

if 判断语句

if后面不需要写括号，编译器会自动去掉
语句内容必须有大括号“{}”

package mainimport "fmt"func main() {//if后面不需要写括号，编译器会自动去掉//语句内容必须有大括号“{}”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")}
}

for 循环语句（只有for）

Go语言中只有for循环语句

package mainimport "fmt"func main() {i := 1for {fmt.Println("loop")break}for j := 0; j < 10; 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}
}

switch 选择语句

package mainimport ("fmt""time"
)func main() {a := 2switch 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")}//可以使用任意类型变量写switcht := time.Now()switch {case t.Hour() < 12:fmt.Println("It's before noon")default:fmt.Println("It's after noon")}
}

数组（较少使用）

固定长度

package mainimport "fmt"func main() {var a [5]inta[4] = 100fmt.Println(a[4], len(a))b := [5]int{1, 2, 3, 4, 5}fmt.Println(b)var twoD [2][3]intfor i := 0; i < 2; i++ {for j := 0; j < 3; j++ {twoD[i][j] = i + j}}fmt.Println("2d: ", twoD)
}

切片（较多使用）

动态长度

package mainimport "fmt"func main() {s := make([]string, 3)s[0] = "a"s[1] = "b"s[2] = "c"fmt.Println("get:", s[2])   //get: cfmt.Println("len:", len(s)) //len: 3s = 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（实际最常用）

完全无序，随机输出

package mainimport "fmt"func main() {m := make(map[string]int)m["one"] = 1m["two"] = 2fmt.Println(m)           //map[one:1 two:2]fmt.Println(len(m))      // 2fmt.Println(m["one"])    // 1fmt.Println(m["unknow"]) // 0r, ok := m["unknow"] //0 flasefmt.Println(r, ok)delete(m, "one") //删除m2 := map[string]int{"one": 1, "two": 2}var m3 = map[string]int{"one": 1, "two": 2}fmt.Println(m2, m3) //map[one:1 two:2] map[one:1 two:2]
}

range

package mainimport "fmt"func main() {nums := []int{2, 3, 4}sum := 0for i, num := range nums {sum += numif num == 2 {fmt.Println("index:", i, "num:", num) // index: 0 num: 2}}fmt.Println(sum) // 9m := 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 mainimport "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) // 3v, ok := exists(map[string]string{"a": "A"}, "a")fmt.Println(v, ok) // A True
}

指针

package mainimport "fmt"func add2(n int) {n += 2
}func add2ptr(n *int) {*n += 2
}func main() {n := 5add2(n)fmt.Println(n) // 5add2ptr(&n)fmt.Println(n) // 7
}

结构体

package mainimport "fmt"type user struct {name     stringpassword string
}func main() {a := user{name: "wang", password: "1024"}b := user{"wang", "1024"}c := user{name: "wang"}c.password = "1024"var d userd.name = "wang"d.password = "1024"fmt.Println(a, b, c, d)                 // {wang 1024} {wang 1024} {wang 1024} {wang 1024}fmt.Println(checkPassword(a, "haha"))   // falsefmt.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 mainimport "fmt"type user struct {name     stringpassword 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
}

错误处理

package mainimport ("errors""fmt"
)type user struct {name     stringpassword 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) // wangif u, err := findUser([]user{{"wang", "1024"}}, "li"); err != nil {fmt.Println(err) // not foundreturn} else {fmt.Println(u.name)}
}

字符串操作

package mainimport ("fmt""strings"
)func main() {a := "hello"fmt.Println(strings.Contains(a, "ll"))                // truefmt.Println(strings.Count(a, "l"))                    // 2fmt.Println(strings.HasPrefix(a, "he"))               // truefmt.Println(strings.HasSuffix(a, "llo"))              // truefmt.Println(strings.Index(a, "ll"))                   // 2fmt.Println(strings.Join([]string{"he", "llo"}, "-")) // he-llofmt.Println(strings.Repeat(a, 2))                     // hellohellofmt.Println(strings.Replace(a, "e", "E", -1))         // hEllofmt.Println(strings.Split("a-b-c", "-"))              // [a b c]fmt.Println(strings.ToLower(a))                       // hellofmt.Println(strings.ToUpper(a))                       // HELLOfmt.Println(len(a))                                   // 5b := "你好"fmt.Println(len(b)) // 6
}

字符串格式化

package mainimport "fmt"type point struct {x, y int
}func main() {s := "hello"n := 123p := point{1, 2}fmt.Println(s, n) // hello 123fmt.Println(p)    // {1 2}fmt.Printf("s=%v\n", s)  // s=hellofmt.Printf("n=%v\n", n)  // n=123fmt.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 := 3.141592653fmt.Println(f)          // 3.141592653fmt.Printf("%.2f\n", f) // 3.14
}

JSON操作

只要结构体的每个成员第一个字母都是大写，这个结构体就可以使用json.Marshal方法序列化，输出时想要小写的成员名就加上 'json:"age"'
打印时需要做string转换

package mainimport ("encoding/json""fmt"
)type userInfo struct {Name  stringAge   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 userInfoerr = 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

不同于Java YYYY-MM-dd的方法，go语言用特定时间指示格式

package mainimport ("fmt""time"
)func main() {now := time.Now()fmt.Println(now) // 2022-03-27 18:04:59.433297 +0800 CST m=+0.000087933t := 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 UTCfmt.Println(t.Year(), t.Month(), t.Day(), t.Hour(), t.Minute()) // 2022 March 27 1 25fmt.Println(t.Format("2006-01-02 15:04:05"))                    // 2022-03-27 01:25:36diff := t2.Sub(t)fmt.Println(diff)                           // 1h5m0sfmt.Println(diff.Minutes(), diff.Seconds()) // 65 3900t3, err := time.Parse("2006-01-02 15:04:05", "2022-03-27 01:25:36")if err != nil {panic(err)}fmt.Println(t3 == t)    // truefmt.Println(now.Unix()) // 1648738080
}

数字解析

strconv.ParseInt（）中的参数，10表示10进制，写0的情况下自动推测，64表示精度

package mainimport ("fmt""strconv"
)func main() {f, _ := strconv.ParseFloat("1.234", 64)fmt.Println(f) // 1.234n, _ := strconv.ParseInt("111", 10, 64)fmt.Println(n) // 111n, _ = strconv.ParseInt("0x1000", 0, 64)fmt.Println(n) // 4096n2, _ := strconv.Atoi("123")fmt.Println(n2) // 123n2, err := strconv.Atoi("AAA")fmt.Println(n2, err) // 0 strconv.Atoi: parsing "AAA": invalid syntax
}

进程信息

package mainimport ("fmt""os""os/exec"
)func main() {// go run example/20-env/main.go a b c dfmt.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
}