golang小结 2

array, slice, map

遍历

    for k,v:=range m { //v可省
        fmt.Println(k,v)
    }

数组

• 一维数组定义

  var arr1 = [4]int{1, 2, 3}
  var arr2 = [...]int{1, 2, 3}
  fmt.Printf("%T, %v, %d %d\n", arr1, arr1, len(arr1), cap(arr1))
  fmt.Printf("%T, %v, %d %d\n", arr2, arr2, len(arr2), cap(arr2))
  /*
  [4]int, [2 3 4 0], 4 4
  [3]int, [1 2 3], 3 3
  */
  

• 多维数组定义

  var arr1 = [3][2]int{{1, 2},
      {3, 4},
      {5, 6},
  }
  fmt.Println(arr1, len(arr1), len(arr1[0])
  //[[1 2] [3 4] [5 6]] 3 2
  )
  

• 注意事项

  • 数组不能更改长度

      //arr1 = append(arr1, 2)
      //arr1 = [5]int{3, 4, 5}
    

  • 数组是值类型，赋值会进行完整拷贝

    func foo(x [3]int, y []int) {
        fmt.Println(&x[0], &y[0])
    }
    func test3() {
        arr1 := [...]int{1, 2, 3}
        fmt.Println(&arr1[0])
        foo(arr1, arr1[:])
    }
    //0xc042008440
    //0xc042008480 0xc042008440
    

  • 程序在运行时会自动对数组进行越界检查

切片

• 构造切片

  var s1 []int = []int{1, 2}
  var s2 = make([]int, 10，20)
  var s3 = make([]int, 10)
  // make内置函数，是可重载的特例 make(type, len, cap=len)
  a := [...]int{1, 2, 3, 4, 5}
  var s4 = a[1:3] //切片名称的由来，底层数组相同
  var s5 = append([]int{}, a[1:3]...)//底层数组不同，可变参数的使用
  

• 切片修改

  //增加
  s2 = append(s2,1)
  s2 = append(s2, s1...)
  //增加有可能会更换底层数组
  //删除
  index:=5
  s2 = append(s2[:index],s2[index+1:])
  //插入
  r = append([]int,s2[index:]...)//必须重新分配个临时空间
  s2 = append(s2[:index],123)
  s2 = append(s2, r...)
  //拷贝 copy(dst,src) 拷贝大小为两者len的最小值
  func testcopy() {
      s1 := []int{1, 2, 3}
      s2 := []int{4, 5}
      copy(s1, s2)
      fmt.Println(s1)
      s1 = []int{7, 8, 9}
      copy(s2, s1)
      fmt.Println(s2)
  }
  /*
  [4 5 3]
  [7 8]
  */
  

• 注意事项

  • 切片是引用类型。对切片内元素的更改，会对底层数组造成更改，对底层数组的更改，也会造成对切片元素的更改
  • 对于同时使用底层数组，或切片共享底层数组时需特别注意

字典

func test1() {
    a := map[string]int{"abc": 1,
        "cda": 2,
    }//构造
    a["haha"] = 4//插入
    delete(a, "abc")//删除
    for k, _ := range a {//_可省
        fmt.Println(k, a[k])
    }
    b := make(map[int]string, 2)// make(type, cap=0) 指定cap应该有所优化
    b[3] = "good"
    fmt.Println(b)
}
func test2() {
    for i := 0; i < 5; i++ {
    m := map[int]string{
        0: "a", 1: "a", 2: "a", 3: "a", 4: "a",
        5: "a", 6: "a", 7: "a", 8: "a", 9: "a",
    }
    fmt.Println(m)//map[int] 的实现方式不一定是有序的，每次遍历的结果可能不一样
    for k := range m {
        m[k+k] = "x"//插入或修改
        delete(m, k)
    }
    fmt.Println(m)
    }
}
/*
cda 2
haha 4
map[3:good]
map[1:a 3:a 5:a 9:a 0:a 2:a 4:a 6:a 7:a 8:a]
map[8:x 18:x 48:x 14:x 2:x 6:x 10:x 32:x]
map[0:a 5:a 6:a 7:a 9:a 1:a 2:a 3:a 4:a 8:a]
map[18:x 24:x 4:x 20:x 16:x 6:x 28:x]
map[1:a 2:a 4:a 6:a 0:a 5:a 7:a 8:a 9:a 3:a]
map[10:x 18:x 28:x 6:x 2:x 16:x 24:x]
map[0:a 2:a 5:a 8:a 1:a 3:a 4:a 6:a 7:a 9:a]
map[6:x 14:x 2:x 8:x 12:x 20:x 18:x 32:x]
map[8:a 9:a 0:a 3:a 6:a 5:a 7:a 1:a 2:a 4:a]
map[18:x 12:x 10:x 14:x 2:x 16:x]
*/

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