go_Map

go语言中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类型不包括上述字段，也可作为key

map中的key是无序的

package main
 
import (
	"fmt"
	"sort"
)
 
var (
	barVal = map[string]int{"alpha": 34, "bravo": 56, "charlie": 23,
		"delta": 87, "echo": 56, "foxtrot": 12,
		"golf": 34, "hotel": 16, "indio": 87,
		"juliet": 65, "kili": 43, "lima": 98}
)
func main() {
	m:=map [string]string {
		"name":"fyf",
		"course":"golang",
		"site":"imooc",
		"quality":"notbad",
	}
 
	m2:=make(map[string]int)//空map一般就用make定义 m2==empty map
 
	var m3 map[string]string//m3 == nil
	fmt.Println(m,m2,m3)
	fmt.Println("")
 
	//map的遍历
	fmt.Println("map的遍历")
	for k,v :=range m{
		fmt.Println(k,v)
	}
	fmt.Println("")
 
	//mao的操作
	fmt.Println("得到value")
	//如果map中的key不存在，则会得到一个nil值
	courseName:=m["course"]
	fmt.Println(courseName)
	//判断key是否存在map中
	courseName2,ok:=m["course"]
	fmt.Println(courseName2,ok)
	if couseName,ok:=m["couse"]; ok{
		fmt.Println(couseName)
	}else {
		fmt.Println("key 不存在")
	}
 
	fmt.Println("")
	fmt.Println("删除value")
	name,ok:=m["name"]
	fmt.Println(name,ok)
 
	delete(m,"name")
	name,ok = m["name"]
	fmt.Println(name,ok)
 
	fmt.Println("unsorted:")
	for k, v := range barVal {
		fmt.Printf("Key: %v, Value: %v / ", k, v)
	}
	keys := make([]string, len(barVal))
	i := 0
	for k, _ := range barVal {
		keys[i] = k//往数组里面放值
		i++
	}
	fmt.Println("")
	fmt.Println("")
	fmt.Println(keys)
	sort.Strings(keys)
	fmt.Println()
	fmt.Println("sorted:")
	for _, k := range keys {
		fmt.Printf("Key: %v, Value: %v / ", k, barVal[k])
	}
 
	fmt.Println("")
	fmt.Println("")
	items := make([]map[int]int, 5)
	for i:= range items {
		items[i] = make(map[int]int, 1)
		items[i][1] = 2//key is 1, value is 2
	}
	fmt.Printf("Version A: Value of items: %v\n", items)
}