go语言map取值 Go 语言Map(集合)

Map 是一种无序的键值对的集合。Map 最重要的一点是通过 key 来快速检索数据，key 类似于索引，指向数据的值。

Map 是一种集合，所以我们可以像迭代数组和切片那样迭代它。不过，Map 是无序的，我们无法决定它的返回顺序，这是因为 Map 是使用 hash 表来实现的。

定义 Map

可以使用内建函数 make 也可以使用 map 关键字来定义 Map:

var map_variable map[key_data_type]value_data_type


map_variable = make(map[key_data_type]value_data_type)

如果不初始化 map，那么就会创建一个 nil map。nil map 不能用来存放键值对

实例

下面实例演示了创建和使用map:

package main

import "fmt"

func main() {
   var countryCapitalMap map[string]string
   
   countryCapitalMap = make(map[string]string)
   
   
   countryCapitalMap["France"] = "Paris"
   countryCapitalMap["Italy"] = "Rome"
   countryCapitalMap["Japan"] = "Tokyo"
   countryCapitalMap["India"] = "New Delhi"
   
   
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }
   
   
   captial, ok := countryCapitalMap["United States"]
   
   if(ok){
      fmt.Println("Capital of United States is", captial)  
   }else {
      fmt.Println("Capital of United States is not present") 
   }
}

以上实例运行结果为：

Capital of France is Paris
Capital of Italy is Rome
Capital of Japan is Tokyo
Capital of India is New Delhi
Capital of United States is not present

delete() 函数

delete() 函数用于删除集合的元素, 参数为 map 和其对应的 key。实例如下：

package main

import "fmt"

func main() {   
   
   countryCapitalMap := map[string] string {"France":"Paris","Italy":"Rome","Japan":"Tokyo","India":"New Delhi"}
   
   fmt.Println("原始 map")   
   
   
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }
   
   
   delete(countryCapitalMap,"France");
   fmt.Println("Entry for France is deleted")  
   
   fmt.Println("删除元素后 map")   
   
   
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }
}

以上实例运行结果为：

原始 map
Capital of France is Paris
Capital of Italy is Rome
Capital of Japan is Tokyo
Capital of India is New Delhi
Entry for France is deleted
删除元素后 map
Capital of Italy is Rome
Capital of Japan is Tokyo
Capital of India is New Delhi