Go Fast Learning-08-map

This is a creation in Article, where the information may have evolved or changed.

Directory

• • Map
    • Create a Map
    • Setter and Getter
    • Size
    • Delete an element
    • Map nesting
    • Check if key exists
    • Traverse

Summary

Create Map,make,setter,getter,size,delete, check the existence of keys, traverse

Map

Create a Map

Define and then initialize

varmap[int]stringmap[int]string{}   //m1 map[]

Using the Make function

Format is

make([keyType]valueType, cap)Capacity can be omitted

varmap[int]stringmake(map[int]string)

Use shorthand

make(map[int]string)

Setter and Getter

Setter

m3[1"a"     //m3 map[1:a]

The "1" Here is a key, not an index

Getter

a := m3[1]b := m3[2]fmt.Println("a"//a afmt.Println("b"//b

Returns NULL when a nonexistent key is obtained

Size

varlen(m3)

Delete an element

delete(m3, 1)fmt.Println("a", a)   //a afmt.Println("m3"//m3 map[]

Map nesting

The Value of a map is another map

varMMap[int]Map[int]string= Make(Map[int]Map[int]string) m[1] = Make(Map[int]string) m[1][1] ="a"Fmt. Println ("M", m)//m Map[1:map[1:a]]Fmt. Println ("m[1]"M[1])//m[1] map[1:a]

Check if key exists

When you use shorthand to return multiple values at the same time, the second parameter that the map returns is a Boolean value that indicates whether the key exists

m3[1"a"m3[2"b"v, exist := m3[3]           //第二个参数为布尔值，表示键是否存在fmt.Println("v", v)         //vfmt.Println("exist"//exist false

Traverse

forrange m3 {    fmt.Println(k, v)}

where k is the key, if you want to ignore the use of K can use the placeholder "_"

//Ignore value  for  k: = range  w {fmt. Print (k)}//ignore key  for  _, V: = range  w {fmt. Print (v)}