スライス

スライス

func main() {
    n := []int{1, 2, 3, 4, 5, 6}
    fmt.Println(n)      //[1 2 3 4 5 6]
    fmt.Println(n[2])   //3
    fmt.Println(n[2:4]) //[3 4]
    fmt.Println(n[2:])  //[3 4 5 6]
    fmt.Println(n[:2])  //[1 2]
    fmt.Println(n[2:3]) //[3]
    fmt.Println(n[:])   //[1 2 3 4 5 6]

    n[2] = 1234
    fmt.Println(n) //[1 2 1234 4 5 6]

    //入れ子構造(スライスの中にスライス)
    var board = [][]int{
        []int{0, 1, 2},
        []int{3, 4, 5},
        []int{6, 7, 8},
    }
    fmt.Println(board) //[[0 1 2] [3 4 5] [6 7 8]]

    n = append(n, 100, 200, 300, 400)
    fmt.Println(n) //[1 2 1234 4 5 6 100 200 300 400]
}

スライスのmakeとcap

func main() {
    n := make([]int, 3, 5)
    fmt.Printf("len=%d cap=%d value=%v\n", len(n), cap(n), n) //len=3 cap=5 value=[0 0 0]
    n = append(n, 0, 0)
    fmt.Printf("len=%d cap=%d value=%v\n", len(n), cap(n), n) //len=5 cap=5 value=[0 0 0 0 0]
    n = append(n, 1, 2, 3, 4, 5)
    fmt.Printf("len=%d cap=%d value=%v\n", len(n), cap(n), n) //len=11 cap=12 value=[0 0 0 0 0 1 2 3 4 5]

    a := make([]int, 3)                                        //引数1つだけとると長さとキャパシティが3
    fmt.Printf("leng=%d cap=%d value=%v\n", len(a), cap(a), a) //leng=3 cap=3 value=[0 0 0]

    b := make([]int, 0)                                       //0のスライスをメモリに確保
    var c []int                                               //メモリ確保しないnil
    fmt.Printf("len=%d cap=%d value=%v\n", len(b), cap(b), b) //len=0 cap=0 value=[]
    fmt.Printf("len=%d cap=%d value=%v\n", len(c), cap(c), c) //len=0 cap=0 value=[]

    c = make([]int, 5)
    for i := 0; i < 5; i++ {
        c = append(c, i)
        fmt.Println(c)
    }
    fmt.Println(c)
    //結果
    // [0 0 0 0 0 0]
    // [0 0 0 0 0 0 1]
    // [0 0 0 0 0 0 1 2]
    // [0 0 0 0 0 0 1 2 3]
    // [0 0 0 0 0 0 1 2 3 4]
    // [0 0 0 0 0 0 1 2 3 4]

    c = make([]int, 0, 5)
    for i := 0; i < 5; i++ {
        c = append(c, i)
        fmt.Println(c)
    }
    fmt.Println(c)
    //結果
    // [0]
    // [0 1]
    // [0 1 2]
    // [0 1 2 3]
    // [0 1 2 3 4]
    // [0 1 2 3 4]
}