go 切片
切片定义
切片是基于数组类型做的一层封装。它非常灵活，可以自动扩容。
var a []int //定义一个int类型的空切片
切片初始化, a[start:end]创建一个包括从start到end-1的切片。
package main import ( "fmt" ) func main() { a := [5]int{76, 77, 78, 79, 80} var b []int = a[1:4] //基于数组a创建⼀个切⽚，包括元素a[1] a[2] a[3] fmt.Println(b) }
切片初始化方法2
package main import ( "fmt" ) func main() { c := []int{6, 7, 8} //创建⼀个数组并返回⼀个切⽚ fmt.Println(c) }
数组切片的基本操作
切片基本操作
a) arr[start:end]：包括start到end-1(包括end-1)之间的所有元素
b) arr[start:]：包括start到arr最后一个元素(包括最后一个元素)之间的所有元素
c) arr[:end]：包括0到end-1(包括end-1）之间的所有元素
d) arr[:]：包括整个数组的所有元素
package main import ( "fmt" ) func testSlice0() { var a []int if a == nil { fmt.Printf("a is nil\n") } else { fmt.Printf("a = %v\n", a) } a[0] = 100 } func testSlice1() { a := [5]int{1, 2, 3, 4, 5} var b []int b = a[1:4] fmt.Printf("slice b:%v\n", b) fmt.Printf("b[0]=%d\n", b[0]) fmt.Printf("b[1]=%d\n", b[1]) fmt.Printf("b[2]=%d\n", b[2]) fmt.Printf("b[3]=%d\n", b[3]) } func testSlice2() { a := []int{1, 2, 3, 4, 5} fmt.Printf("slice a:%v type of a:%T\n", a, a) } func testSlice3() { a := [5]int{1, 2, 3, 4, 5} var b []int b = a[1:4] fmt.Printf("slice b:%v\n", b) // c := a[1:len(a)] c := a[1:] fmt.Printf("slice c:%v\n", c) //d := a[0:3] d := a[:3] fmt.Printf("slice d:%v\n", d) // e := a[0:len(a)] e := a[:] fmt.Printf("slice e:%v\n", e) } func testSlice4() { a := [...]int{1, 2, 3, 4, 5, 7, 8, 9, 11} fmt.Printf("array a:%v type of a:%T\n", a, a) b := a[2:5] fmt.Printf("slice b:%v type of b:%T\n", b, b) /* b[0] = b[0] + 10 b[1] = b[1] + 20 b[2] = b[2] + 30 */ /* for index, val := range b { fmt.Printf("b[%d]=%d\n", index, val) } */ for index := range b { b[index] = b[index] + 10 } fmt.Printf("after modify slice b, array a:%v type of a:%T\n", a, a) } func testSlice5() { a := [...]int{1, 2, 3} s1 := a[:] s2 := a[:] s1[0] = 100 fmt.Printf("a=%v s2=%v\n", a, s2) s2[1] = 200 fmt.Printf("a=%v s1=%v\n", a, s1) } func main() { //testSlice0() //testSlice1() //testSlice2() //testSlice3() //testSlice4() testSlice5() }
切片修改
package main import ( "fmt" ) func main() { //创建一个数组，其中[…]是编译器确定数组的⻓度,darr的长度是9 darr := [...]int{57, 89, 90, 82, 100, 78, 67, 69, 59} //基于darr创建一个切片dslice,包括darr[2],darr[3],darr[4]三个元素 dslice := darr[2:5] fmt.Println("array before",darr) for i := range dslice { //对于dslice中每个元素进行+1，其实修改是darr[2],darr[3],darr[4] dslice[i]++ } fmt.Println("array after",darr) }
package main import ( "fmt" ) func main() { numa := [3]int{78, 79 ,80} //创建一个切片，包含整个数组的所有元素 nums1 := numa[:] nums2 := numa[:] fmt.Println("array before change 1",numa) nums1[0] = 100 fmt.Println("array after modification to slice nums1", numa) nums2[1] = 101 fmt.Println("array after modification to slice nums2", numa) }
使用make创建切片
package main import ( "fmt" ) func main() { //[]中没有长度 i := make([]int, 5, 5) fmt.Println(i) }
切片的长度和容量
package main import ( "fmt" ) func main() { fruitarray := […]string{ "apple", "orange", "grape", "mango", "water melon", "pine apple", "chikoo"} fruitslice := fruitarray[1:3] //长度是2，容量is 6 fmt.Printf("length of slice %d capacity %d", len(fruitslice), cap(fruitslice)) }
package main import "fmt" func testMake1() { var a []int a = make([]int, 5, 10) a[0] = 10 //a[1] = 20 fmt.Printf("a=%v addr:%p len:%d cap:%d\n", a, a, len(a), cap(a)) a = append(a, 11) fmt.Printf("a=%v addr:%p len:%d cap:%d\n", a, a, len(a), cap(a)) for i := 0; i < 8; i++ { a = append(a, i) fmt.Printf("a=%v addr:%p len:%d cap:%d\n", a, a, len(a), cap(a)) } //观察切片的扩容操作，扩容的策略是翻倍扩容 a = append(a, 1000) fmt.Printf("扩容之后的地址：a=%v addr:%p len:%d cap:%d\n", a, a, len(a), cap(a)) } /* a=[10 0 0 0 0] addr:0xc0000860a0 len:5 cap:10 a=[10 0 0 0 0 11] addr:0xc0000860a0 len:6 cap:10 a=[10 0 0 0 0 11 0] addr:0xc0000860a0 len:7 cap:10 a=[10 0 0 0 0 11 0 1] addr:0xc0000860a0 len:8 cap:10 a=[10 0 0 0 0 11 0 1 2] addr:0xc0000860a0 len:9 cap:10 a=[10 0 0 0 0 11 0 1 2 3] addr:0xc0000860a0 len:10 cap:10 a=[10 0 0 0 0 11 0 1 2 3 4] addr:0xc000098000 len:11 cap:20 a=[10 0 0 0 0 11 0 1 2 3 4 5] addr:0xc000098000 len:12 cap:20 a=[10 0 0 0 0 11 0 1 2 3 4 5 6] addr:0xc000098000 len:13 cap:20 a=[10 0 0 0 0 11 0 1 2 3 4 5 6 7] addr:0xc000098000 len:14 cap:20 扩容之后的地址：a=[10 0 0 0 0 11 0 1 2 3 4 5 6 7 1000] addr:0xc000098000 len:15 cap:20 */ func testMake2() { var a []int a = make([]int, 5, 10) //a[5] = 100 a = append(a, 10) fmt.Printf("a=%v\n", a) b := make([]int, 0, 10) fmt.Printf("b=%v len:%d cap:%d\n", b, len(b), cap(b)) b = append(b, 100) fmt.Printf("b=%v len:%d cap:%d\n", b, len(b), cap(b)) } func main() { // testMake1() testMake2() }
切片的再切片
package main import "fmt" func reslice() { a := [...]int{1, 2, 3, 4, 5, 6, 4, 7, 8} b := a[2:4] fmt.Printf("b = %d len(b) = %d cap(b)=%d\n", b, len(b), cap(b)) c := b[:cap(b)] fmt.Printf("c = %d len(c) = %d cap(c)=%d\n", c, len(c), cap(c)) } func main() { reslice() } /* b = [3 4] len(b) = 2 cap(b)=7 c = [3 4 5 6 4 7 8] len(c) = 7 cap(c)=7 */
计算容量
package main import "fmt" func testCap() { a := [...]int{1, 2, 3, 4, 5, 6, 7} b := a[1:3] fmt.Print("b= %v len(b) = %d, cap(b) = %d\n", b, len(b), cap(b)) // 切片的容量 等于 原始素组的长度 减去 切片开始的索引 } func main() { testCap() }
package main import ( "fmt" ) func main() { fruitarray := […]string{ "apple", "orange", "grape", "mango", "water melon", "pine apple", "chikoo"} fruitslice := fruitarray[1:3] //⻓度是2, 容量是6 fmt.Printf("length of slice %d capacity %d\n", len(fruitslice), cap(fruitslice)) //再重新进⾏切⽚，不能⼤于数组fruitarray的⻓度，否则越界 fruitslice = fruitslice[:cap(fruitslice)] fmt.Println("After re-slicing length is”, len(fruitslice), "and capacity is",cap(fruitslice)) }
append操作
package main import ( "fmt" ) func main() { cars := []string{"Ferrari", "Honda", "Ford"} //长度和容量都等于3 fmt.Println("cars:", cars, "has old length", len(cars), "and capacity", cap(cars)) cars = append(cars, "Toyota") //容量等于6 fmt.Println("cars:", cars, "has new length", len(cars), "and capacity", cap(cars)) } /* cars: [Ferrari Honda Ford] has old length 3 and capacity 3 cars: [Ferrari Honda Ford Toyota] has new length 4 and capacity 6 */
空切片
package main import ( "fmt" ) func main() { //定义names是一个空切片，长度和容量都等于0 //不能对空切片进行访问，否则panic var names []string if names == nil { fmt.Println("slice is nil going to append") names = append(names, "John", "Sebastian", "Vinay") fmt.Println("names contents:",names) } }
package main import "fmt" func test() { var a []int fmt.Printf("addr = %p len=%d cap =%d\n", a, len(a), cap(a)) // a[0]=100 报错 if a == nil { fmt.Printf("a is nil\n") } a = append(a, 100) fmt.Printf("addr = %p len=%d cap =%d\n", a, len(a), cap(a)) a = append(a, 200) fmt.Printf("addr = %p len=%d cap =%d\n", a, len(a), cap(a)) a = append(a, 300) fmt.Printf("addr = %p len=%d cap =%d\n", a, len(a), cap(a)) a = append(a, 400) fmt.Printf("addr = %p len=%d cap =%d\n", a, len(a), cap(a)) } /* addr = 0x0 len=0 cap =0 a is nil addr = 0xc0000100e0 len=1 cap =1 addr = 0xc000010100 len=2 cap =2 addr = 0xc00000a3c0 len=3 cap =4 addr = 0xc00000a3c0 len=4 cap =4 */ func main() { test() }
append一个切片
package main import ( "fmt" ) func main() { veggies := []string{"potatoes","tomatoes","brinjal"} fruits := []string{"oranges","apples"} //fruits后面的3个点表示展开fruits切片成一个个元素 food := append(veggies, fruits...) fmt.Println("food:",food) } // food: [potatoes tomatoes brinjal oranges apples]
package main import "fmt" func test() { var a []int = []int{1, 2, 3} b := []int{4, 5, 6} c := append(a, b...) fmt.Printf("a=%v\n", a) fmt.Printf("b=%v\n", b) fmt.Printf("c=%v\n", c) } /* a=[1 2 3] b=[4 5 6] c=[1 2 3 4 5 6] */ func main() { test() }
切片传参
package main import ( "fmt" ) //在函数内部修改numbers切⽚的值 func subtactOne(numbers []int) { for i := range numbers { numbers[i] -= 2 } } func main() { nos := []int{8, 7, 6} fmt.Println("slice before function call", nos) subtactOne(nos) //nos修改生效了，说明切片是引用类型 fmt.Println("slice after function call", nos) } /* slice before function call [8 7 6] slice after function call [6 5 4] */
package main import "fmt" func testSum(a []int) int { sum := 0 for _, v := range a { sum += v } return sum } func testChange(a []int) { a[0] = 1000 } func main() { a := [...]int{1, 2, 3, 4, 5, 6} // sum := testSum(a[:]) // fmt.Printf("sum = %d", sum) // 21 fmt.Printf("a=%v\n", a) testChange(a[:]) fmt.Printf("a=%v", a) /* a=[1 2 3 4 5 6] a=[1000 2 3 4 5 6] */ }
切片拷贝
package main import ( "fmt" ) func main() { veggies := []string{"potatoes", "tomatoes", "brinjal"} fruits := []string{"oranges", "apples"} copy(veggies, fruits) fmt.Println(veggies, fruits) //[oranges apples brinjal] [oranges apples] }
package main import "fmt" func testCopy() { a := []int{1, 2, 3} b := []int{4, 5, 6} copy(a, b) fmt.Printf("a = %v\n", a) // [4,5,6] fmt.Printf("b = %v\n", b) // [4,5,6] c := []int{1, 2} d := []int{4, 5, 6} e := copy(c, d) fmt.Printf("c = %v\n", c) // [4,5] fmt.Printf("d = %v\n", d) // [4,5,6] fmt.Printf("e = %v\n", e) // 2 b[0] = 100 fmt.Printf("a = %v\n", a) // [4,5,6] fmt.Printf("b = %v\n", b) // [100 5 6] aa := [...]int{1, 2, 3, 4, 5, 6} bb := aa[:] cc := []int{10, 20, 30} copy(bb, cc) fmt.Printf("aa = %v\n", aa) // [10 20 30 4 5 6] fmt.Printf("bb = %v\n", bb) // [10 20 30 4 5 6] fmt.Printf("cc = %v\n", cc) // [10 20 30] } func main() { testCopy() }
切片遍历
var a [3]int a[0] = 10 a[1] = 20 a[2] = 30 b := a[:] for index, val := range b { } //和数组遍历一样
make和new区别
make为内建类型slice、map和channel分配内存。
//初始化一个切片 s := make([]int, 10, 30)
new用于各种类型的内存分配，new返回是一个指针。
