Go语言学习——map

var data map[int]string  //只是声明一个map，没有初始化, 此为空(nil)map
fmt.Println(data == nil) //true
//data[1] = "apple" //err, panic: assignment to entry in nil map

//data2, data3的创建方法是等价的
data2 := map[int]string{}
data3 := make(map[int]string)
fmt.Println(data2, data3) //map[] map[]

data4 := make(map[int]string, 10) //第2个参数指定容量
fmt.Println(data4)                //map[]

3.1、定义同时初始化

var data map[int]string = map[int]string{1: "apple", 2: "banana"}
fmt.Println(data) //map[1:apple 2:banana]

3.2、自动推导类型 :=

data2 := map[int]string{1: "apple", 2: "banana"}
fmt.Println(data2)

data := map[int]string{1: "apple", 2: "banana"}
data[1] = "xxx"   //修改
data[3] = "pear"  //追加， go底层会自动为map分配空间
fmt.Println(data) //map[1:xxx 2:banana 3: pear]

data2 := make(map[int]string
4000
, 10) //创建map
data2[0] = "aaa"
data2[1] = "bbb"
fmt.Println(data2)           //map[0:aaa 1:bbb]

data := map[int]string{1: "apple", 2: "banana"}
//迭代遍历1，第一个返回值是key，第二个返回值是value
for k, v := range data {
fmt.Printf("%d ----> %s\n", k, v)
//1 ----> apple
//2 ----> banana
}

//迭代遍历2，第一个返回值是key，第二个返回值是value（可省略）
for k := range data {
fmt.Printf("%d ----> %s\n", k, data[k])
//1 ----> apple
//2 ----> banana
}

//判断某个key所对应的value是否存在, 第一个返回值是value(如果存在的话)
value, ok := data[1]
fmt.Println("value = ", value, ", ok = ", ok) //value =  apple , ok =  true

value2, ok2 := data[3]
fmt.Println("value2 = ", value2, ", ok2 = ", ok2) //value2 =   , ok2 =  false

data := map[int]string{1: "apple", 2: "banana", 3: "pear"}
//迭代遍历1，第一个返回值是key，第二个返回值是value
for k, v := range data {
fmt.Printf("%d ----> %s\n", k, v)
//1 ----> apple
//2 ----> banana
//3 ----> pear
}

delete(data, 2) //删除key值为2的map

for k, v := range data {
fmt.Printf("%d ----> %s\n", k, v)
//1 ----> apple
//3 ----> pear
}