golang语言渐入佳境[17]-mapping表

2025-01-22 技术教程

mapping 声明

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//1、声明map的方式1
var map1 map[string]string

//2、声明map的方式2
map2 := make(map[string]string)

//3、map中key可以是：int、float、bool、string、数组
//一定不可以是：切片、函数、map
var m1 map[int]string
var m2 map[float64]string
var m3 map[bool]string
var m4 map[string]string
mapping定义与初始化

1、声明时同时初始化

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var country = map[string]string{
"China": "Beijing",
"Japan": "Tokyo",
"India": "New Delhi",
"France": "Paris",
"Italy": "Rome",
}
fmt.Println(country)

//短变量声明初始化方式
rating := map[string]float64{"c": 5, "Go": 4.5, "Python": 4.5, "C++": 3}
fmt.Println(rating)

2、创建map后再赋值

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countryMap := make(map[string]string)
countryMap["China"] = "Beijing"
countryMap["Japan"] = "Tokyo"
countryMap["India"] = "New Delhi"
countryMap["France"] = "Paris"
countryMap["Italy"] = "Rome"
mapping遍历(1)、key 、value都遍历

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for k, v := range countryMap {
fmt.Println("国家", k, "首都", v)
}
(2)、只展示value

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for _, v := range countryMap {
fmt.Println("国家", "首都", v)
}
(3)、只展示key

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for k := range countryMap {
fmt.Println("国家", k , "首都", countryMap[k])
}
(4)、查看元素是否在map中存在

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value , ok := countryMap["England"]
fmt.Printf("%q \n" , value)
fmt.Printf("%T , %v \n" , ok , ok)
if ok {
fmt.Println("首都：" , value)
} else {
fmt.Println("首都信息未检索到！")
}

//第二种方式
if value ,ok :=countryMap["USA"];ok {
fmt.Println("首都：" , value)
} else {
fmt.Println("首都信息未检索到！")
}
完整代码

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package main

import "fmt"

func main() {
//1、声明时同时初始化
var country = map[string]string{
"China": "Beijing",
"Japan": "Tokyo",
"India": "New Delhi",
"France": "Paris",
"Italy": "Rome",
}
fmt.Println(country)

//短变量声明初始化方式
rating := map[string]float64{"c": 5, "Go": 4.5, "Python": 4.5, "C++": 3}
fmt.Println(rating)

//2、创建map后再赋值
countryMap := make(map[string]string)
countryMap["China"] = "Beijing"
countryMap["Japan"] = "Tokyo"
countryMap["India"] = "New Delhi"
countryMap["France"] = "Paris"
countryMap["Italy"] = "Rome"

//3、遍历map（无序）
//(1)、key 、value都遍历
for k, v := range countryMap {
fmt.Println("国家", k, "首都", v)
}
fmt.Println("-----------")

//(2)、只展示value
for _, v := range countryMap {
fmt.Println("国家", "首都", v)
}
fmt.Println("-----------")

//(3)、只展示key
for k := range countryMap {
fmt.Println("国家", k , "首都", countryMap[k])
}
fmt.Println("-----------")

//4、查看元素是否在map中存在
value , ok := countryMap["England"]
fmt.Printf("%q \n" , value)
fmt.Printf("%T , %v \n" , ok , ok)
if ok {
fmt.Println("首都：" , value)
} else {
fmt.Println("首都信息未检索到！")
}

//或者
if value ,ok :=countryMap["USA"];ok {
fmt.Println("首都：" , value)
} else {
fmt.Println("首都信息未检索到！")
}
}
mapping 删除

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package main

import "fmt"

func main() {
//1、声明并初始化一个map
map1 := map[string]string {
"element":"div",
"width" :"100px",
"height":"200px",
"border":"solid",
"background":"none",
}

//2、根据key删除map中的某个元素
fmt.Println("删除前：",map1)
if _,ok := map1["background"]; ok {
delete(map1 , "background")
}
fmt.Println("删除后：",map1)

//3、清空map
//map1 = map[string]string{}
map1 = make(map[string]string)
fmt.Println("清空后：",map1)
}