golang中的map 详解

map是一种无序的基于kay-value的数据结构，Go语言中的map是引用类型，必须初始化才能使用。
go语言中map的定于语法如下：
```
map[keyType]valueType
```
其中：
* KeyType 表示键的类型
* valueType 表示键对应的值的类型

## 定义map
map类型的变量默认初始值为nil，需要使用make()函数来分配内存。语法为：
**make: 用于slice，map和channel 的初始化**
```
func main() {
	var mymap = make(map[string]string)
	mymap["key1"] = "value1"
	mymap["key2"] = "value2"
	fmt.Printf("mymap: %v\n", mymap)

// map在声明时填充元素
	var mymap1 = map[string]string{
		"keys1": "values1",
		"keys2": "values2",
		"keys3": "values3",
	}
	fmt.Printf("mymap1: %v\n", mymap1)
	//第三种 声明map的方法
	mymap2 := map[string]string{
		"keys1": "values1",
		"keys2": "values2",
		"keys3": "values3",
	}
	fmt.Printf("mymap2: %v\n", mymap2)
}
```

## 遍历map
```
func main() {

mymap2 := map[string]string{
		"keys1": "values1",
		"keys2": "values2",
		"keys3": "values3",
	}
	for _, v := range mymap2 {
		fmt.Printf("v: %v\n", v)
		/*
			v: values3
			v: values1
			v: values2
		*/
	}
}
```

## map crud
```
func main() {
	//创建map
	var mymap = map[string]string{
		"username": "haha",
		"age":      "20",
	}
	//查找keys
	s := mymap["age"]
	fmt.Printf("s: %v\n", s) //s: 20
	//更新values
	mymap["age"] = "30"
	fmt.Printf("mymap[\"age\"]: %v\n", mymap["age"]) //mymap["age"]: 30
	//删除 keys
	delete(mymap, "age")
	fmt.Printf("mymap: %v\n", mymap) //mymap: map[username:haha]
}
```

## slice 中存入 map类型的数据
```
func main() {
	var myslice = make([]map[string]string, 3, 3)
	myslice[0] = map[string]string{
		"username": "haha",
		"age":      "23",
	}
	myslice[1] = map[string]string{
		"username1": "haha1",
		"age":       "23",
	}

fmt.Printf("myslice: %v\n", myslice)

}
```
遍历
```
func main() {
	var myslice = make([]map[string]string, 3, 3)
	myslice[0] = map[string]string{
		"username": "haha",
		"age":      "23",
	}
	myslice[1] = map[string]string{
		"username1": "haha1",
		"age":       "23",
	}

fmt.Printf("myslice: %v\n", myslice)

for _, v := range myslice {
		for map_k, map_v := range v {
			fmt.Printf("map_k: %v\t", map_k)
			fmt.Printf("map_v: %v\n", map_v)
		}
	}
}
```

## 值为slice 的 map
```
unc main() {
	var mymap = map[string][]string{
		"key1": []string{"haha", "haha1", "haha2"},
		"key2": []string{"haha3", "haha4", "a急急急"},
	}

fmt.Printf("mymap: %v\n", mymap)
	for k, v := range mymap {
		fmt.Printf("k: %v\n", k)
		for _, slice_v := range v {
			fmt.Printf("slice_v: %v\n", slice_v)
		}
	}

}
/*
k: key1
slice_v: haha
slice_v: haha1
slice_v: haha2
k: key2
slice_v: haha3
slice_v: haha4
slice_v: a急急急
*/
```
## 判断是否存在
```
m := make(map[string]string)
	m["test1"] = "test1"
	m["test2"] = "test2"

for k, v := range m {
		fmt.Printf("%v  %v \n", k, v)
	}
	value, exists := m["test1"]
	fmt.Printf("value %v  exists %v", value, exists)
	//value test1  exists true
```