Go

Kevin2li大约 7 分钟Language

简介

参考：
https://gobyexample.com/open in new window

语法

Hello World

package main

import "fmt"

func main() {
    fmt.Println("hello world")
}

变量

变量声明

package main

import "fmt"

func main() {

    var a = "initial"
    fmt.Println(a)

    var b, c int = 1, 2
    fmt.Println(b, c)

    var d = true
    fmt.Println(d)

    var e int
    fmt.Println(e)

    f := "apple"
    fmt.Println(f)
}

常量声明

package main

import (
    "fmt"
    "math"
)

const s string = "constant"

func main() {
    fmt.Println(s)

    const n = 500000000

    const d = 3e20 / n
    fmt.Println(d)

    fmt.Println(int64(d))

    fmt.Println(math.Sin(n))
}

数据类型

字符串

package main

import (
    "fmt"
    "unicode/utf8"
)

func main() {

    const s = "สวัสดี"
    
    // 获取字符串长度
    fmt.Println("Len:", len(s))

    // 遍历字符串
    for i := 0; i < len(s); i++ {
        fmt.Printf("%x ", s[i])
    }
    fmt.Println()
    
    // 统计rune数量
    fmt.Println("Rune count:", utf8.RuneCountInString(s))

    // 遍历字符串
    for idx, runeValue := range s {
        fmt.Printf("%#U starts at %d\n", runeValue, idx)
    }
}

格式化输出

package main

import (
    "fmt"
    "os"
)

type point struct {
    x, y int
}

func main() {

    p := point{1, 2}
    fmt.Printf("struct1: %v\n", p)

    fmt.Printf("struct2: %+v\n", p)

    fmt.Printf("struct3: %#v\n", p)

    fmt.Printf("type: %T\n", p)

    fmt.Printf("bool: %t\n", true)

    fmt.Printf("int: %d\n", 123)

    fmt.Printf("bin: %b\n", 14)

    fmt.Printf("char: %c\n", 33)

    fmt.Printf("hex: %x\n", 456)

    fmt.Printf("float1: %f\n", 78.9)

    fmt.Printf("float2: %e\n", 123400000.0)
    fmt.Printf("float3: %E\n", 123400000.0)

    fmt.Printf("str1: %s\n", "\"string\"")

    fmt.Printf("str2: %q\n", "\"string\"")

    fmt.Printf("str3: %x\n", "hex this")

    fmt.Printf("pointer: %p\n", &p)

    fmt.Printf("width1: |%6d|%6d|\n", 12, 345)

    fmt.Printf("width2: |%6.2f|%6.2f|\n", 1.2, 3.45)

    fmt.Printf("width3: |%-6.2f|%-6.2f|\n", 1.2, 3.45)

    fmt.Printf("width4: |%6s|%6s|\n", "foo", "b")

    fmt.Printf("width5: |%-6s|%-6s|\n", "foo", "b")

    s := fmt.Sprintf("sprintf: a %s", "string")
    fmt.Println(s)

    fmt.Fprintf(os.Stderr, "io: an %s\n", "error")
}

输出：

struct1: {1 2}
struct2: {x:1 y:2}
struct3: main.point{x:1, y:2}
type: main.point
bool: true
int: 123
bin: 1110
char: !
hex: 1c8
float1: 78.900000
float2: 1.234000e+08
float3: 1.234000E+08
str1: "string"
str2: "\"string\""
str3: 6865782074686973
pointer: 0xc0000ba000
width1: |    12|   345|
width2: |  1.20|  3.45|
width3: |1.20  |3.45  |
width4: |   foo|     b|
width5: |foo   |b     |
sprintf: a string
io: an error

数组

package main

import "fmt"

func main() {

    var a [5]int
    fmt.Println("emp:", a)

    a[4] = 100
    fmt.Println("set:", a)
    fmt.Println("get:", a[4])

    fmt.Println("len:", len(a))

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

切片

package main

import "fmt"

func main() {
    
    // 声明切片
    s := make([]string, 3)
    fmt.Println("emp:", s)

    // 赋值和访问
    s[0] = "a"
    s[1] = "b"
    s[2] = "c"
    fmt.Println("set:", s)
    fmt.Println("get:", s[2])
    
    // 获取切片长度
    fmt.Println("len:", len(s))

    // 切片追加元素
    s = append(s, "d")
    s = append(s, "e", "f")
    fmt.Println("apd:", s)

    // 拷贝切片
    c := make([]string, len(s))
    copy(c, s)
    fmt.Println("cpy:", c)

    // 切片子集
    l := s[2:5]
    fmt.Println("sl1:", l)

    l = s[:5]
    fmt.Println("sl2:", l)

    l = s[2:]
    fmt.Println("sl3:", l)

    t := []string{"g", "h", "i"}
    fmt.Println("dcl:", t)

    twoD := make([][]int, 3)
    for i := 0; i < 3; i++ {
        innerLen := i + 1
        twoD[i] = make([]int, innerLen)
        for j := 0; j < innerLen; j++ {
            twoD[i][j] = i + j
        }
    }
    fmt.Println("2d: ", twoD)
}

字典

package main

import "fmt"

func main() {

    m := make(map[string]int)

    m["k1"] = 7
    m["k2"] = 13

    fmt.Println("map:", m)

    v1 := m["k1"]
    fmt.Println("v1:", v1)

    v3 := m["k3"]
    fmt.Println("v3:", v3)

    fmt.Println("len:", len(m))

    delete(m, "k2")
    fmt.Println("map:", m)

    _, prs := m["k2"]
    fmt.Println("prs:", prs)

    n := map[string]int{"foo": 1, "bar": 2}
    fmt.Println("map:", n)
}

结构体

package main

import "fmt"

type person struct {
    name string
    age  int
}

func newPerson(name string) *person {

    p := person{name: name}
    p.age = 42
    return &p
}

func main() {

    fmt.Println(person{"Bob", 20})

    fmt.Println(person{name: "Alice", age: 30})

    fmt.Println(person{name: "Fred"})

    fmt.Println(&person{name: "Ann", age: 40})

    fmt.Println(newPerson("Jon"))

    s := person{name: "Sean", age: 50}
    fmt.Println(s.name)

    sp := &s
    fmt.Println(sp.age)

    sp.age = 51
    fmt.Println(sp.age)
}

控制流

条件

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() {

    i := 2
    fmt.Print("Write ", i, " as ")
    switch i {
    case 1:
        fmt.Println("one")
    case 2:
        fmt.Println("two")
    case 3:
        fmt.Println("three")
    }

    switch time.Now().Weekday() {
    case time.Saturday, time.Sunday:
        fmt.Println("It's the weekend")
    default:
        fmt.Println("It's a weekday")
    }

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

    whatAmI := func(i interface{}) {
        switch t := i.(type) {
        case bool:
            fmt.Println("I'm a bool")
        case int:
            fmt.Println("I'm an int")
        default:
            fmt.Printf("Don't know type %T\n", t)
        }
    }
    whatAmI(true)
    whatAmI(1)
    whatAmI("hey")
}

循环

for

package main
import "fmt"

func main() {
    
    // 经典for
    for n := 0; n <= 5; n++ {
        if n%2 == 0 {
            continue
        }
        fmt.Println(n)
    }
    
    // 使用range遍历数组
    nums := []int{2, 3, 4}
    sum := 0
    for _, num := range nums {
        sum += num
    }
    fmt.Println("sum:", sum)

    for i, num := range nums {
        if num == 3 {
            fmt.Println("index:", i)
        }
    }
    
    // 使用range遍历字典
    kvs := map[string]string{"a": "apple", "b": "banana"}
    for k, v := range kvs {
        fmt.Printf("%s -> %s\n", k, v)
    }
    
    // 只遍历key
    for k := range kvs {
        fmt.Println("key:", k)
    }

    // 使用range遍历字符串
    for i, c := range "go" {
        fmt.Println(i, c)
    }
    
}

函数

普通函数

package main

import "fmt"

func plus(a int, b int) int {

    return a + b
}

func plusPlus(a, b, c int) int {
    return a + b + c
}

func main() {

    res := plus(1, 2)
    fmt.Println("1+2 =", res)

    res = plusPlus(1, 2, 3)
    fmt.Println("1+2+3 =", res)
}

多返回值

package main

import "fmt"

func vals() (int, int) {
    return 3, 7
}

func main() {

    a, b := vals()
    fmt.Println(a)
    fmt.Println(b)

    _, c := vals()
    fmt.Println(c)
}

变长参数列表

package main

import "fmt"

func sum(nums ...int) {
    fmt.Print(nums, " ")
    total := 0

    for _, num := range nums {
        total += num
    }
    fmt.Println(total)
}

func main() {

    sum(1, 2)
    sum(1, 2, 3)

    nums := []int{1, 2, 3, 4}
    sum(nums...)
}

指针

package main

import "fmt"

func zeroval(ival int) {
    ival = 0
}

func zeroptr(iptr *int) {
    *iptr = 0
}

func main() {
    i := 1
    fmt.Println("initial:", i)

    zeroval(i)
    fmt.Println("zeroval:", i)

    zeroptr(&i)
    fmt.Println("zeroptr:", i)

    fmt.Println("pointer:", &i)
}

输出：

initial: 1
zeroval: 1
zeroptr: 0
pointer: 0x42131100

面向对象

方法

package main

import "fmt"

type rect struct {
    width, height int
}

func (r *rect) area() int {
    return r.width * r.height
}

func (r rect) perim() int {
    return 2*r.width + 2*r.height
}

func main() {
    r := rect{width: 10, height: 5}

    fmt.Println("area: ", r.area())
    fmt.Println("perim:", r.perim())

    rp := &r
    fmt.Println("area: ", rp.area())
    fmt.Println("perim:", rp.perim())
}

接口

package main

import (
    "fmt"
    "math"
)

type geometry interface {
    area() float64
    perim() float64
}

type rect struct {
    width, height float64
}
type circle struct {
    radius float64
}

func (r rect) area() float64 {
    return r.width * r.height
}
func (r rect) perim() float64 {
    return 2*r.width + 2*r.height
}

func (c circle) area() float64 {
    return math.Pi * c.radius * c.radius
}
func (c circle) perim() float64 {
    return 2 * math.Pi * c.radius
}

func measure(g geometry) {
    fmt.Println(g)
    fmt.Println(g.area())
    fmt.Println(g.perim())
}

func main() {
    r := rect{width: 3, height: 4}
    c := circle{radius: 5}

    measure(r)
    measure(c)
}

并发

标准库函数

文件路径

package main

import (
    "fmt"
    "path/filepath"
    "strings"
)

func main() {

    p := filepath.Join("dir1", "dir2", "filename")
    fmt.Println("p:", p)

    fmt.Println(filepath.Join("dir1//", "filename"))
    fmt.Println(filepath.Join("dir1/../dir1", "filename"))

    fmt.Println("Dir(p):", filepath.Dir(p))
    fmt.Println("Base(p):", filepath.Base(p))

    fmt.Println(filepath.IsAbs("dir/file"))
    fmt.Println(filepath.IsAbs("/dir/file"))

    filename := "config.json"

    ext := filepath.Ext(filename)
    fmt.Println(ext)

    fmt.Println(strings.TrimSuffix(filename, ext))

    rel, err := filepath.Rel("a/b", "a/b/t/file")
    if err != nil {
        panic(err)
    }
    fmt.Println(rel)

    rel, err = filepath.Rel("a/b", "a/c/t/file")
    if err != nil {
        panic(err)
    }
    fmt.Println(rel)
}

文件读取

package main

import (
    "bufio"
    "fmt"
    "io"
    "os"
)

func check(e error) {
    if e != nil {
        panic(e)
    }
}

func main() {

    dat, err := os.ReadFile("/tmp/dat")
    check(err)
    fmt.Print(string(dat))

    f, err := os.Open("/tmp/dat")
    check(err)

    b1 := make([]byte, 5)
    n1, err := f.Read(b1)
    check(err)
    fmt.Printf("%d bytes: %s\n", n1, string(b1[:n1]))

    o2, err := f.Seek(6, 0)
    check(err)
    b2 := make([]byte, 2)
    n2, err := f.Read(b2)
    check(err)
    fmt.Printf("%d bytes @ %d: ", n2, o2)
    fmt.Printf("%v\n", string(b2[:n2]))

    o3, err := f.Seek(6, 0)
    check(err)
    b3 := make([]byte, 2)
    n3, err := io.ReadAtLeast(f, b3, 2)
    check(err)
    fmt.Printf("%d bytes @ %d: %s\n", n3, o3, string(b3))

    _, err = f.Seek(0, 0)
    check(err)

    r4 := bufio.NewReader(f)
    b4, err := r4.Peek(5)
    check(err)
    fmt.Printf("5 bytes: %s\n", string(b4))

    f.Close()
}

文件写入

package main

import (
    "bufio"
    "fmt"
    "os"
)

func check(e error) {
    if e != nil {
        panic(e)
    }
}

func main() {

    d1 := []byte("hello\ngo\n")
    err := os.WriteFile("/tmp/dat1", d1, 0644)
    check(err)

    f, err := os.Create("/tmp/dat2")
    check(err)

    defer f.Close()

    d2 := []byte{115, 111, 109, 101, 10}
    n2, err := f.Write(d2)
    check(err)
    fmt.Printf("wrote %d bytes\n", n2)

    n3, err := f.WriteString("writes\n")
    check(err)
    fmt.Printf("wrote %d bytes\n", n3)

    f.Sync()

    w := bufio.NewWriter(f)
    n4, err := w.WriteString("buffered\n")
    check(err)
    fmt.Printf("wrote %d bytes\n", n4)

    w.Flush()

}

排序

package main

import (
    "fmt"
    "sort"
)

func main() {

    strs := []string{"c", "a", "b"}
    sort.Strings(strs)
    fmt.Println("Strings:", strs)

    ints := []int{7, 2, 4}
    sort.Ints(ints)
    fmt.Println("Ints:   ", ints)

    s := sort.IntsAreSorted(ints)
    fmt.Println("Sorted: ", s)
}

时间格式化

package main

import (
    "fmt"
    "time"
)

func main() {
    p := fmt.Println

    t := time.Now()
    p(t.Format(time.RFC3339))

    t1, e := time.Parse(
        time.RFC3339,
        "2012-11-01T22:08:41+00:00")
    p(t1)

    p(t.Format("3:04PM"))
    p(t.Format("Mon Jan _2 15:04:05 2006"))
    p(t.Format("2006-01-02T15:04:05.999999-07:00"))
    form := "3 04 PM"
    t2, e := time.Parse(form, "8 41 PM")
    p(t2)

    fmt.Printf("%d-%02d-%02dT%02d:%02d:%02d-00:00\n",
        t.Year(), t.Month(), t.Day(),
        t.Hour(), t.Minute(), t.Second())

    ansic := "Mon Jan _2 15:04:05 2006"
    _, e = time.Parse(ansic, "8:41PM")
    p(e)
}

json处理

package main

import (
    "encoding/json"
    "fmt"
    "os"
)

type response1 struct {
    Page   int
    Fruits []string
}

type response2 struct {
    Page   int      `json:"page"`
    Fruits []string `json:"fruits"`
}

func main() {

    bolB, _ := json.Marshal(true)
    fmt.Println(string(bolB))

    intB, _ := json.Marshal(1)
    fmt.Println(string(intB))

    fltB, _ := json.Marshal(2.34)
    fmt.Println(string(fltB))

    strB, _ := json.Marshal("gopher")
    fmt.Println(string(strB))

    slcD := []string{"apple", "peach", "pear"}
    slcB, _ := json.Marshal(slcD)
    fmt.Println(string(slcB))

    mapD := map[string]int{"apple": 5, "lettuce": 7}
    mapB, _ := json.Marshal(mapD)
    fmt.Println(string(mapB))

    res1D := &response1{
        Page:   1,
        Fruits: []string{"apple", "peach", "pear"}}
    res1B, _ := json.Marshal(res1D)
    fmt.Println(string(res1B))

    res2D := &response2{
        Page:   1,
        Fruits: []string{"apple", "peach", "pear"}}
    res2B, _ := json.Marshal(res2D)
    fmt.Println(string(res2B))

    byt := []byte(`{"num":6.13,"strs":["a","b"]}`)

    var dat map[string]interface{}

    if err := json.Unmarshal(byt, &dat); err != nil {
        panic(err)
    }
    fmt.Println(dat)

    num := dat["num"].(float64)
    fmt.Println(num)

    strs := dat["strs"].([]interface{})
    str1 := strs[0].(string)
    fmt.Println(str1)

    str := `{"page": 1, "fruits": ["apple", "peach"]}`
    res := response2{}
    json.Unmarshal([]byte(str), &res)
    fmt.Println(res)
    fmt.Println(res.Fruits[0])

    enc := json.NewEncoder(os.Stdout)
    d := map[string]int{"apple": 5, "lettuce": 7}
    enc.Encode(d)
}

参考