Golang Study notes -1.14 Maps

This is the 14th chapter of Golang Language Learning Tutorial

What is maps?

A map is a built-in type that associates a key (key) with a value in go. The value can be obtained by the corresponding key.

Create a map

makeYou can create a map by passing in the type of key and value to the function. make(map[type of key]type of value) is the syntax for creating a map.

money := make(map[string]int)

The above creates a map named, where the type of the money key is string , the type of the value is int .

Map initial value is empty, need to add element to map

Adding elements to a map

The syntax and arrays for adding elements to a map are the same.
Example 1:

package mainimport "fmt"func main()  {    money := make(map[string]int) //创建 一个名为 money 的 map    money["xunk"] = 20000    money["ergou"] = 30000    money["jobs"] = 40000   //给 money 添加元素    fmt.Println("money's map is ", money)}

The above program output is:money's map is map[xunk:20000 ergou:30000 jobs:40000]
You can also initialize the map at the time of declaration.
Example 2:

package mainimport "fmt"func main()  {    money := map[string]int {        "xunk" : 2000,        "ergou" : 3000,        "jobs" : 4000,    }    money["bill"] = 6000    fmt.Println("money's map is ", money)}

The above program adds three elements when declaring a map, and then adds Bill, which outputs:
money's map is map[xunk:2000 ergou:3000 jobs:4000 bill:6000]

Keys are not necessarily only string types. All comparable types, such as boolean,interger,float,complex,string, can be used as keys.

Get the elements in a map

The element syntax for getting map is:map[key]

package mainimport "fmt"//make(map(type of key)type of value)func main()  {    money := map[string]int {  //声明时添加值        "xunk" : 2000,        "ergou" : 3000,        "jobs" : 4000,    }    money["bill"] = 6000    name := "jobs"    fmt.Println("the money of ", name, "is ", money[name])}

The above procedure obtains the amount of jobs and prints them out. The program output is:the money of jobs is 4000

If you get a nonexistent element, map returns a 0 value of the element for that type. As in the procedure above, we get a nonexistent key that returns int the value of the type 0 .

    money := map[string]int {  //声明时添加值        "xunk" : 2000,        "ergou" : 3000,        "jobs" : 4000,    }    money["bill"] = 6000    fmt.Println("the money of danny is ", money["danny"])}

The program output is:the money of danny is 0

To see if the key exists in the map, the syntax is:value, ok := map[key]

    money := map[string]int {  //声明时添加值        "xunk" : 2000,        "ergou" : 3000,        "jobs" : 4000,    }    money["bill"] = 6000    newname := "jenny"    value, ok := money[newname]    if ok == true {        fmt.Println("jenny's money is ", value)    } else {        fmt.Println(newname,"not found")    }}

In the above program, if ok = True, it means that the key exists, the corresponding value is value , and vice versa does not exist.
The program output is:
jenny not found

Iterating through the elements in the map requires a for range loop:

    for key, value  := range money{        fmt.Printf("map[%s] = %d\n", key, value)    }

The above program output is:

Map[xunk] = 2000
Map[ergou] = 3000
Map[jobs] = 4000
Map[bill] = 6000

Delete an element in a map

Deleting the element syntax in map is: delete(map,key) This function does not return a value.

book := map[string]int {        "bainiangudu" : 3,        "fooled" : 2,        "blockchain" : 1,    }    delete(book, "bainiangudu")    fmt.Println(book)}

The above program removed the key bainiangudu , the program output is:
map[fooled:2 blockchain:1]

Map is a reference type

Like slice, map is also a reference type, and when a map is assigned a new variable, they point to the same internal data structure, and when one of the variables is changed, it affects the other.

    newmoney := money    newmoney["xunk"] = 5000    fmt.Println(money["xunk"])

In the above program, the value will be assigned to money newmoney , then change newmoney the value in xunk , then money the xunk values also change. The program output is:
5000

The above for learning Golang Maps Chapter