Go Map映射

Go提供了另一种重要的数据类型，称为映射（map），它将唯一的键映射到值。键是您用于稍后检索值的对象。给定一个键和一个值，您可以将该值存储在一个Map对象中。在值被存储后，您可以通过使用键来检索它。

定义一个Map

您必须使用 make 函数来创建一个映射。

/* declare a variable, by default map will be nil*/
var map_variable map[key_data_type]value_data_type

/* define the map as nil map can not be assigned any value*/
map_variable = make(map[key_data_type]value_data_type)

示例

下面的示例说明了如何创建和使用地图 –

package main

import "fmt"

func main() {
   var countryCapitalMap map[string]string
   /* create a map*/
   countryCapitalMap = make(map[string]string)

   /* insert key-value pairs in the map*/
   countryCapitalMap["France"] = "Paris"
   countryCapitalMap["Italy"] = "Rome"
   countryCapitalMap["Japan"] = "Tokyo"
   countryCapitalMap["India"] = "New Delhi"

   /* print map using keys*/
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }

   /* test if entry is present in the map or not*/
   capital, ok := countryCapitalMap["United States"]

   /* if ok is true, entry is present otherwise entry is absent*/
   if(ok){
      fmt.Println("Capital of United States is", capital)  
   } else {
      fmt.Println("Capital of United States is not present") 
   }
}

当上述代码被编译和执行时，它产生以下结果 −

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

delete() 函数

delete() 函数用于从映射中删除一个条目。它需要映射和要删除的相应键。例如 –

package main

import "fmt"

func main() {   
   /* create a map*/
   countryCapitalMap := map[string] string {"France":"Paris","Italy":"Rome","Japan":"Tokyo","India":"New Delhi"}

   fmt.Println("Original map")   

   /* print map */
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }

   /* delete an entry */
   delete(countryCapitalMap,"France");
   fmt.Println("Entry for France is deleted")  

   fmt.Println("Updated map")   

   /* print map */
   for country := range countryCapitalMap {
      fmt.Println("Capital of",country,"is",countryCapitalMap[country])
   }
}

当上述代码被编译和执行时，将产生以下结果 −

Original 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
Updated Map
Capital of India is New Delhi
Capital of Italy is Rome
Capital of Japan is Tokyo