Go map基础

 package main

 import "fmt"

 //Map
 //创建：make(map[string]int)
 //获取元素： m[key]
 //key不存在时，获得value类型的初始值
 //用value， ok:= m[key]来判断是否存在key
 //delete删除元素
 //用range遍历key，或者遍历key，value对
 //不保证遍历顺序，如需顺序，需手动对key排序
 //用len获得元素个数
 //map使用哈希表，必须可以比较相等
 //除了slice， map, function的内建类型都可以作为key
 //struct类型不包含上述字段也可以作为key

 func main() {
     //创建map
     m := map[string] string {
         "name": "ccmouse" ,
         "course": "golang",
         "site": "imooc",
         "quality": "notbad",
     }
     fmt.Println(m) //map[course:golang site:imooc quality:notbad name:ccmouse]

     m2 := make( map[string]int)
     fmt.Println(m2)  //map[]  m2 == empty map

     var m3 map[string]int
     fmt.Println(m3)  //map[]  m3 == nil

     //map的遍历
     for k, v := range m{
         fmt.Println(k, v)   //name ccmouse //hash map输出无序
                             //course golang
                             //site imooc
                             //quality notbad
     }

     //map取值
     courseName, ok := m["course"]
     fmt.Println(courseName, ok)  //golang true

     if causeName, ok:= m["cause"]; ok{  //判断值存不存在
         fmt.Println(causeName)
     }else{
         fmt.Println("Key does not exist")   //Key does not exist
     }

     //删除元素
     name, ok := m["name"]
     fmt.Println(name, ok)  //ccmouse true
     delete(m, "name")
     name, ok = m["name"]
     fmt.Println(name, ok)  // false
 }