七、Map声明、元素访问及遍历

Map声明

m := map[string]int{"one":1,"two":2,"three":3}

m1 := map[string]int{}

m1["one"] = 1

m2 := make(map[string]int, 10 /*Initial Capacity*/)

Map元素的访问

在访问的Key不存在时，仍会返回零值，不能通过返回nil来判断元素是否存在

func TestAccessNotExistingKey(t *testing.T) {
	m1 := map[int]int{}
	t.Log(m1[1])
	m1[2] = 0
	t.Log(m1[2])
	m1[3] = 0 //可以注释此行代码查看运行结果
	if v,ok:=m1[3];ok{
		t.Logf("key 3's value is %d",v)
	}else {
		t.Log("key 3 is not existing.")
	}
}

输出

=== RUN   TestAccessNotExistingKey
--- PASS: TestAccessNotExistingKey (0.00s)
    map_test.go:20: 0
    map_test.go:22: 0
    map_test.go:25: key 3's value is 0
PASS

Process finished with exit code 0

Map 遍历

示例代码

m := map[string]int{"one":1,"two":2,"three":3}
for k, v := range m {
  t.Log(k, v)
}

func TestTracelMap(t *testing.T) {
	m1 := map[int]int{1: 1, 2: 4, 3: 9}
	for k, v := range m1 {
		t.Log(k, v)
	}
}

输出

=== RUN   TestTracelMap
--- PASS: TestTracelMap (0.00s)
    map_test.go:34: 1 1
    map_test.go:34: 2 4
    map_test.go:34: 3 9
PASS

Process finished with exit code 0