【go学习笔记】六、数组和切片

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

最新动态

示例代码请访问： https://github.com/wenjianzhang/golearning