【go学习笔记】六、数组和切片【连载】

数组的声明

var a [3]int // 声明并初始化为默认零值
a[0] = 1

b := [3]int{1,2,3}          //声明同时初始化
c := [2][2]int{{1,2},{3,4}} //多维数组初始化

数组元素遍历

func testarraytravel(t *testing.t) {
    arr3 := [...]int{1, 3, 4, 5}
    for i := 0; i < len(arr3); i++ {
        t.log(arr3[i])
    }

    for idx, e := range arr3 {
        t.log(idx, e)
    }
}

输出

=== run   testarraytravel
--- pass: testarraytravel (0.00s)
    array_test.go:17: 1
    array_test.go:17: 3
    array_test.go:17: 4
    array_test.go:17: 5
    array_test.go:21: 0 1
    array_test.go:21: 1 3
    array_test.go:21: 2 4
    array_test.go:21: 3 5
pass

process finished with exit code 0

数组截取

a[开始索引(包含),结束索引(不包含)]

a := [...]int{1, 2, 3, 4, 5}
a[1:2] // 2
a[1:3] // 2,3
a[1:len(a)] // 2,3,4,5
a[:3] // 1,2,3

示例代码

func testarraysection(t *testing.t)  {
    arr3 := [...]int{1, 2, 3, 4, 5}
    arr_sec :=arr3[3:]
    t.log(arr_sec)
}

输出

=== run   testarraysection
--- pass: testarraysection (0.00s)
    array_test.go:28: [4 5]
pass

process finished with exit code 0

切片内部结构

• 切片是一个结构体
• 第一个参数是指针，指向一个数组（连续存储空间）
• 元素个数
• 容量

package slice_test

import "testing"

func testsliceinit(t *testing.t) {
    var s0 []int
    t.log(len(s0), cap(s0))
    s0 = append(s0, 1)
    t.log(len(s0), cap(s0))

    s1 := []int{1, 2, 3, 4}
    t.log(len(s1), cap(s1))

    s2 := make([]int, 3, 5)
    t.log(len(s2), cap(s2))
    //t.log(s2[0], s2[1], s2[3], s2[4])
    //panic: runtime error: index out of range [recovered]
    //panic: runtime error: index out of range

    t.log(s2[0], s2[1], s2[2])

    s2 = append(s2, 1)
    t.log(s2[0], s2[1], s2[2], s2[3])
    t.log(len(s2), cap(s2))

}

输出

=== run   testsliceinit
--- pass: testsliceinit (0.00s)
    slice_test.go:7: 0 0
    slice_test.go:9: 1 1
    slice_test.go:12: 4 4
    slice_test.go:15: 3 5
    slice_test.go:20: 0 0 0
    slice_test.go:23: 0 0 0 1
    slice_test.go:24: 4 5
pass

process finished with exit code 0

切片共享存储结构

func testslicesharememory(t *testing.t) {
    year := []string{"jan", "feb", "mar", "apr", "may", "jun", "jul", "aug", "sep", "oct","nov", "dec"}
    q2 := year[3:6]
    t.log(q2, len(q2), cap(q2))

    summer := year[5:8]
    t.log(summer, len(summer), cap(summer))
    summer[0] = "unknow"
    t.log(q2)
    t.log(year)
}

输出

=== run   testslicesharememory
--- pass: testslicesharememory (0.00s)
    slice_test.go:39: [apr may jun] 3 9
    slice_test.go:42: [jun jul aug] 3 7
    slice_test.go:44: [apr may unknow]
    slice_test.go:45: [jan feb mar apr may unknow jul aug sep oct nov dec]
pass

process finished with exit code 0

数组vs. 切片

1. 容量是否可伸缩
2. 是否可以进行比较

func testslicecompare(t *testing.t) {
    a := []int{1, 2, 3, 4}
    b := []int{1, 2, 3, 4}
    if a == b {
        t.log("equal")
    }
}

输出

# command-line-arguments_test [command-line-arguments.test]
./slice_test.go:51:7: invalid operation: a == b (slice can only be compared to nil)

compilation finished with exit code 2

slice can only be compared to nil