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
}