Go map基础

Posted 2020-12-27 yuxiaoba

 1 package main
 2 
 3 import "fmt"
 4 
 5 //Map
 6 //创建：make(map[string]int)
 7 //获取元素： m[key]
 8 //key不存在时，获得value类型的初始值
 9 //用value， ok:= m[key]来判断是否存在key
10 //delete删除元素
11 //用range遍历key，或者遍历key，value对
12 //不保证遍历顺序，如需顺序，需手动对key排序
13 //用len获得元素个数
14 //map使用哈希表，必须可以比较相等
15 //除了slice， map, function的内建类型都可以作为key
16 //struct类型不包含上述字段也可以作为key
17 
18 func main() {
19     //创建map
20     m := map[string] string {
21         "name": "ccmouse" ,
22         "course": "golang",
23         "site": "imooc",
24         "quality": "notbad",
25     }
26     fmt.Println(m) //map[course:golang site:imooc quality:notbad name:ccmouse]
27 
28     m2 := make( map[string]int)
29     fmt.Println(m2)  //map[]  m2 == empty map
30 
31     var m3 map[string]int
32     fmt.Println(m3)  //map[]  m3 == nil
33 
34     //map的遍历
35     for k, v := range m{
36         fmt.Println(k, v)   //name ccmouse //hash map输出无序
37                             //course golang
38                             //site imooc
39                             //quality notbad
40     }
41 
42     //map取值
43     courseName, ok := m["course"]
44     fmt.Println(courseName, ok)  //golang true
45 
46     if causeName, ok:= m["cause"]; ok{  //判断值存不存在
47         fmt.Println(causeName)
48     }else{
49         fmt.Println("Key does not exist")   //Key does not exist
50     }
51 
52     //删除元素
53     name, ok := m["name"]
54     fmt.Println(name, ok)  //ccmouse true
55     delete(m, "name")
56     name, ok = m["name"]
57     fmt.Println(name, ok)  // false
58 }