Go语言基础: 有参函数Func、Map、Strings详细按理教程

一、Variadic Functions

1.Syntax

	package main
	
	import (
		"fmt"
	)
	
	func Hello(a int, b ...int) {
		fmt.Println(a, b)		// 666 [22 333 555]
	}
	
	func main() {
		Hello(666, 22, 333, 555)
	}

2.Examples and understanding how variadic functions work

	func find(num int, nums ...int) { // 设置一个目标数字与一个 Arrays 查看当前目标数字是否在arrays里面
		fmt.Printf("type of nums is %T\n", nums)
		found := false
		for i, v := range nums { // 循环 Arrays
			if v == num { // 如果值等于 num
				fmt.Println(num, "found at index", i, "in", nums)
				found = true
			}
		}
		if !found {
			fmt.Println(num, "not find in ", nums)
		}
		fmt.Printf("\n")
	}
	
	func main() {
		find(89, 87, 90, 88, 89)		
		find(45, 56, 67, 45, 90, 109)
		find(78, 38, 56, 98)
		find(87)
	}
	
	// type of nums is []int
	// 89 found at index 3 in [87 90 88 89]
	
	
	// 还可以这样调用
	
	
		nums := []int{89, 90, 95}
		find(89, nums) // 如果这样调用则报错 无法运行 需要添加 ...   .\variadic functions. go:33:11: cannot use nums (variable of type []int) as int value in argument to find
		find(89, nums...)	// 89 found at index 0 in [89 90 95]

3.Slice arguments vs Variadic arguments 仅改变可变参数

	func find(num int, nums []int) { // 设置一个目标数字与一个 Arrays 查看当前目标数字是否在arrays里面
		fmt.Printf("type of nums is %T\n", nums)
		found := false
		for i, v := range nums { // 循环 Arrays
			if v == num { // 如果值等于 num
				fmt.Println(num, "found at index", i, "in", nums)
				found = true
			}
		}
		if !found {
			fmt.Println(num, "not find in ", nums)
		}
		fmt.Printf("\n")
	}
	
	func main() {
		find(89, []int{87, 90, 88, 89})
		find(45, []int{56, 67, 45, 90, 109})
		find(78, []int{38, 56, 98})
		find(87, []int{})
	}

4.Gotcha

	package main
	
	import (  
	    "fmt"
	)
	
	func change(s ...string) {
		s[0] = "Go"
		s = append(s, "playground") // append会创建一个新的切片
		fmt.Println(s)              // [Go world playground]
	}
	
	func main() {
		welcome := []string{"hello", "world"}
		change(welcome...)   // change没有受到添加playground的影响 所以它的容量还是2(change操作的是原始的切片, 如果原始切片满了则会创建一个新的切片)
		fmt.Println(welcome) // 所以输出的是 Go world
	}
	
	
	// [Go world playground]
	// [Go world]
	
	
	// Go中的append原始切片如果没有满 则会使用原始切片不会创建新的切片 如果满了则会创建一个新的切片

二、Map

1.Create a Map

	package main
	
	import "fmt"
	
	// create a map
	
	func main() {
		// example 1
		employeeSalary := make(map[string]int)
		fmt.Println(employeeSalary)
		
		// example 2
		Department := map[string]string{
			"Designer": "设计部",
			"Research": "研发部",
		}
		fmt.Println(Department)
		
		// add items to map
		
		employeeSalary["Like"] = 15000
		employeeSalary["Jack"] = 9000
		employeeSalary["Lisa"] = 10000
		fmt.Println("employeeSalary map contents:", employeeSalary)
	
		var employeeSalary map[string]int
		fmt.Println(employeeSalary)
		employeeSalary["Like"] = 15000 	// 不可行 	panic: assignment to entry in nil map
	
	}

2.Retrieving value for a key from a map

	employeeSalary := map[string]int{
			"steve": 12000,
			"jamie": 15000,
			"mike":  9000,
		}

	employee := "jamie"
	salary := employeeSalary[employee]
	fmt.Println("Salary of", employee, "is", salary)		// Salary of jamie is 15000
	fmt.Println("Salary of mike is", employeeSalary["mike"])	// Salary of mike is 9000
	fmt.Println("Salary of joe is", employeeSalary["joe"])	 // Salary of joe is 0 没有则为0

3.Checking if a key exists

	employeeSalary := map[string]int{
		"steve": 12000,
		"jamie": 15000,
		"mike":  9000,
	}

	newEmp := "jamie"
	value, ok := employeeSalary[newEmp] // 0 false
	fmt.Println(value, ok)
	if ok == true {
		fmt.Println(ok)                               // true
		fmt.Println("Salary of", newEmp, "is", value) // Salary of jamie is 15000
		return
	}
	fmt.Println(newEmp, "not Found")

4.Iterate over all elements in a map

	employeeSalary := map[string]int{
		"steve": 12000,
		"jamie": 15000,
		"mike":  9000,
	}

	fmt.Println("Contents of the map")

	for key, value := range employeeSalary {
		fmt.Printf("employessSalary[%s] = %d\n", key, value)
	}

	// 输出
	// Contents of the map
	//employessSalary[steve] = 12000
	//employessSalary[jamie] = 15000
	//employessSalary[mike] = 9000

5. Deleting items from a map

	employeeSalary := map[string]int{
		"steve": 12000,
		"jamie": 15000,
		"mike":  9000,
	}

	fmt.Println("Contents of the map")

	for key, value := range employeeSalary {
		fmt.Printf("employessSalary[%s] = %d\n", key, value)
	}

	// 输出
	// Contents of the map
	//employessSalary[steve] = 12000
	//employessSalary[jamie] = 15000
	//employessSalary[mike] = 9000

6.Map of structs

	package main
	
	import (  
	    "fmt"
	)
	
	type employee struct {  
	    salary  int
	    country string
	}
	
	func main() {  
		emp1 := employee{salary: 6666, country: "Usa"}
		emp2 := employee{salary: 7777, country: "Canada"}
		emp3 := employee{salary: 8888, country: "China"}
		employeeInfo := map[string]employee{
			"Steve": emp1,
			"Lisa":  emp2,
			"Like":  emp3,
		}
	
	    for name, info := range employeeInfo {
	        fmt.Printf("Employee: %s Salary:$%d  Country: %s\n", name, info.salary, info.country)
	    }
	
	}
	
	// Employee: Lisa Salary:$7777  Country: Canada
	// Employee: Like Salary:$8888  Country: China
	// Employee: Steve Salary:$6666  Country: Usa

7.Length of the map

	emp1 := employee{salary: 6666, country: "Usa"}
	emp2 := employee{salary: 7777, country: "Canada"}
	emp3 := employee{salary: 8888, country: "China"}
	employeeInfo := map[string]employee{
	    "Steve": emp1,
	    "Lisa":  emp2,
	    "Like":  emp3,
	}
	
	fmt.Println("length is", len(employeeInfo))
	// length is 3

8.Maps are reference types

	employeeSalary := map[string]int{
		"steve": 12000,
		"jamie": 15000,
		"mike":  9000,
	}
	fmt.Println("Original employee salary", employeeSalary)
	modified := employeeSalary
	modified["mike"] = 18000
	fmt.Println("Employee salary changed", employeeSalary)

	// Original employee salary map[jamie:15000 mike:9000 steve:12000]
	// Employee salary changed map[jamie:15000 mike:18000 steve:12000]	

9.Maps equality

	package main
	
	func main() {  
	    map1 := map[string]int{
	        "one": 1,
	        "two": 2,
	    }
	
	    map2 := map1
	
	    if map1 == map2 {
	    }
	}
	// 不能使用 == 比较 只能判断是否为空

三、Strings

1.Accessing individual bytes of a string

	package main
	
	import "fmt"
	
	func printBytes(s string) {
		fmt.Printf("Bytes:") // 注意go语言不会自动换行
		for i := 0; i < len(s); i++ {
			fmt.Printf("%x ", s[i])
		}
	}
	
	func main() {
		name := "Hello World"
		fmt.Printf("String: %s\n", name)
		printBytes(name)
	}
	
	//	String: Hello World
	//	Bytes:48 65 6c 6c 6f 20 57 6f 72 6c 64

2.Accessing individual characters of a string

	package main
	
	import "fmt"
	
	func printBytes(s string) {
		fmt.Printf("Bytes:") // 注意go语言不会自动换行
		for i := 0; i < len(s); i++ {
			fmt.Printf("%x ", s[i])
		}
	}
	
	func printChars(s string) {
		fmt.Printf("Characters: ")
		runes := []rune(s) // 字符串被转换为一片符文
		for i := 0; i < len(runes); i++ {
			fmt.Printf("%c", runes[i]) // Characters: Hello World
		}
	}
	
	func main() {
		name := "Hello World"
		fmt.Printf("String: %s\n", name)
		printChars(name)
		fmt.Printf("\n")
		printBytes(name)
		fmt.Printf("\n\n")
		name = "Señor" // 特殊字符 如果不转换 则不一致	S e à ± o r
		fmt.Printf("String: %s\n", name)
		printChars(name)
		fmt.Printf("\n")
		printBytes(name)
	}
	
	
	// String: Hello World
	// Characters: Hello World
	// Bytes:48 65 6c 6c 6f 20 57 6f 72 6c 64
	
	// String: Señor
	// Characters: Señor
	// Bytes:53 65 c3 b1 6f 72

3.String length

	word1 := "Señor"
	fmt.Printf("String: %s\n", word1)
	fmt.Printf("Length: %d\n", utf8.RuneCountInString(word1)) // 返回字符数量
	fmt.Printf("Number of bytes: %d\n", len(word1))           // 获取当前字符串长度 	ñ 表示两个

	fmt.Printf("\n")
	word2 := "Pets"
	fmt.Printf("String: %s\n", word2)
	fmt.Printf("Length: %d\n", utf8.RuneCountInString(word2))
	fmt.Printf("Number of bytes: %d\n", len(word2))

4.String comparison

	func compareStrings(str1 string, str2 string) {
		if str1 == str2 {
			fmt.Printf("%s and %s are equal\n", str1, str2)
			return
		}
		fmt.Printf("%s and %s are not equal\n", str1, str2)
	}
	
	string1 := "Go"
	string2 := "Go"
	compareStrings(string1, string2)
	
	string3 := "hello"
	string4 := "world"
	compareStrings(string3, string4)
	
	// Go and Go are equal
	// hello and world are not equal

5.String concatenation

	string1 := "Go"
	string2 := "is awesome"
	//result := string1 + " " + string2
	result := fmt.Sprintf("%s %s", string1, string2)
	fmt.Println(result)

	// Go is awesome

6.Strings are immutable

	func mutate(s string)string {  
	    s[0] = 'a'	//any valid unicode character within single quote is a rune 
	    return s
	}
	func main() {  
	    h := "hello"
	    fmt.Println(mutate(h))		
	}
	
	// 输出 cannot assign to s[0] (value of type byte)
	
	// 优化
	
	func mutate(s []rune) string {  	// mutate函数接受一个[]rune类型的切片作为参数，并返回一个字符串。
	    s[0] = 'a' 					  // []rune是一个Unicode字符的切片类型。它将字符串转换为Unicode字符切片，以便我们可以修改字符串中的字符。
	    return string(s)
	}
	func main() {  
	    h := "hello"
	    fmt.Println(mutate([]rune(h)))	// mutate函数修改了切片中的第一个字符，将其替换为'a'。
	}

四、Printf的%格式化字符串

	%d: 表示有符号十进制整数（int类型）
	%f: 表示浮点数（float32或float64类型）
	%s: 表示字符串
	%t: 表示布尔值（true或false）
	%c: 表示字符（按Unicode码点输出）
	%p: 表示指针地址
	%v: 表示通用的值（以默认方式格式化）
	%+v: 表示结构体值（包含字段名）
	%#v: 表示值的Go语法表示形式
	%x: 表示以十六进制格式输出整数或字节切片
	%b: 表示以二进制格式输出整数
	%o: 表示以八进制格式输出整数
	%e 或 %E: 表示科学计数法表示的浮点数
	%t: 表示以字符串形式输出时间（time.Time类型）
	%T: 表示值的类型（类型的完全规格）
	%10d: 表示输出宽度为10的有符号十进制整数
	%.2f: 表示输出带有两位小数的浮点数
	%05d: 表示输出宽度为5的有符号十进制整数，左侧用零填充