【go学习笔记】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

示例代码请访问：