Go語言學習筆記(十)之切片
阿新 • • 發佈：2018-12-18
-h 種類 一個 fmt advance 小練習 輸出 程序 otto
15.切片
切片是基於數組類型做的一層封裝。它非常靈活，可以自動擴容。
切片的定義
1: var a []int
// 定義一個int類型的空切片
// 切片不初始化是無法操作的，這點和數組不一樣。
切片的初始化：
1: 1.arr[start:end]start到end-1(包括end-1)之間的所有元素2: 2.arr[start:]3: 3.arr[:end]4: 4.arr[:]包括整個數組的所有元素
例：
1: a := [5]int{76,77,78,79,80}2: var b []int = a[1:4]3: c:= []int{6,7,8}
切片的修改：
1: func main() {2: darr := [...]int{57,89,90,82,100,78,67,69,59}3: dslice := darr[2:5]4: fmt.Println("array before", darr)5: for i,_ := range dslice {6: dslice[i] ++7: }8: fmt.Println("array after", darr)9: }
//這種類似於python裏的淺拷貝
1: func main() {2: numa := [3]int{78,79,80}3: nums1 := numa[:]4: nums2 := numa[:]5: fmt.Println("array before change 1", numa)6: nums1[0] = 1007: fmt.Println(numa)8: nums2[1] = 1019: fmt.Println(numa)10: }11: >>> [100 79 80]12: [100 101 80]
使用make創建切片
1: i := make([]int, 5, 5)
// (類型 當前長度 容量上線)
// 未指定的元素默認為0
1: func main() {2: var a []int3: a = make([]int, 1, 10)4: a[0] = 105: // 這裏a[1] = 20 會報錯，操作越界了,這是個重要的細節,忽略很容易犯錯6: a = append(a, 11)7: fmt.Printf(a)8: }
1: >>> [10 11]
擴容(cap(a)是表示a的容量上限)
1: for i:=0;i<10;i++ {2: a = append(a, i)3: fmt.Printf("a=%v addr:%p len:%d cap:%d\n", a,a,len(a),cap(a))4: }
輸出：
1: >>>a=[10 11 0] addr:0xc000014140 len:3 cap:102: a=[10 11 0 1] addr:0xc000014140 len:4 cap:103: a=[10 11 0 1 2] addr:0xc000014140 len:5 cap:104: a=[10 11 0 1 2 3] addr:0xc000014140 len:6 cap:105: a=[10 11 0 1 2 3 4] addr:0xc000014140 len:7 cap:106: a=[10 11 0 1 2 3 4 5] addr:0xc000014140 len:8 cap:107: a=[10 11 0 1 2 3 4 5 6] addr:0xc000014140 len:9 cap:108: a=[10 11 0 1 2 3 4 5 6 7] addr:0xc000014140 len:10 cap:109: a=[10 11 0 1 2 3 4 5 6 7 8] addr:0xc00008a000 len:11 cap:20
//觀察擴容的結果，發現擴容的策略是翻倍擴容
1: func testCap() {2: a := [...]string{"a","b","c","d","e","f","g","h"}3: b := a[1:3]4: fmt.Printf("b:%v len:%d cap:%d\n",b,len(b),cap(b))5: }
1: >>> b:[b c] len:2 cap:7
空切片
1: var a []int2: fmt.Println(a, len(a), cap(a))3: a = append(a, 100)4: fmt.Println(a, len(a), cap(a))
1: >>> [] 0 02: [100] 1 1
切片傳參
1: veggies := []string{"potatoes", "tomatoes", "brinjal"}2: fruits := []string{"oranges", "apples"}3: food := append(veggies, fruits...)4: // friuts後面的3個點表示展開fruits切片成一個個元素5: fmt.Println(food)
1: func modifySlice(a []int) {2: a[0] = 10003: }4: func main(){5: var a [3]int = [3]int{1, 2, 3}6: modifySlice(a[:])7: fmt.Println(a)8: }
1: >>> [1000, 2, 3]
切片的拷貝
1: func main() {2: veggies := []string{"potatoes", "tomatoes", "brinjal"}3: fruits := []string{"oranges", "apples"}4: copy(veggies, fruits)5: fmt.Println(veggies, fruits)6: }
1: >>> [oranges apples brinjal] [oranges apples]
1: func main() {2: var a := []int{1, 2}3: var a = []int{1, 2}4: var b := []int{4, 5, 6}5: copy(a, b)6: fmt.Println(a, b)7: }
1: >>> [4 5] [4 5 6]
make和new的區別
make為內建類型為slice, map和channel分配內存
new用於各種類型的內存分配, new返回的是一個指針
幾個小練習
1.下面程序輸出什麽
1: func main() {2: var a = make([]string, 5, 10);3: for i:=0;i<10;i++{4: a = append(a, fmt.Sprintf("%d", i))5: }6: fmt.Println(a)7: }
1: >>> a= [ ]2: a= [ 0 1 2 3 4 5 6 7 8 9]
2.使用golang標準包"sort"對數組進行排序
1: func main() {2: a := []int{5, 4, 3, 2, 1}3: sort.Ints(a[:])4: fmt.Println("a=",a)5: b := []string{"f", "e", "c", "b", "a"}6: sort.Strings(b[:])7: fmt.Println("b=",b)8: c := []float64{58.554,88.23,998.255,48.25,566.66}9: sort.Float64s(c[:])10: fmt.Println("c=",c)11: }
3.實現一個密碼生成工具，支持以下功能
PS:標準包"flag"解析命令行參數
a.用戶可以通過-l指定生成讓那個密碼的長度
b.用戶可以通過-t指定生成密碼的字符集,比如-t num生成全數字的密碼-t char生成包含全英文字符的密碼, -t mix包含生成數字和英文的密碼,-t advance生成包含數字,英文以及特殊字符的密碼
1: package main2:3: import (4: "fmt"5: "flag"6: "math/rand"7: "time"8: )9: var (10: length int11: charset string12: )13: const (14: NumStr = "0123456789"15: CharStr = "abcdefghjkmnopqrstuvwxyzABCDEFGHJKMNOPQRSTUVWXYZ"16: SpecStr = "@#$%^&*_+=/*-"17: )18: func parseArgs() {19: flag.IntVar(&length, "l", 16, "-l 生成密碼長度")20: flag.StringVar(&charset, "t", "num",21: `-t 制定密碼生成的字符集,22: num:只使用數字[0-9],23: char:只使用英文字母[a-zA-Z],24: mix:使用數字和字母,25: advance：使用數字字母以及特殊字符`)26: flag.Parse()27: }28: func generatePasswd() string {29: var password []byte = make([]byte, length, length)30: var sourceStr string31: if charset == "num" {32: sourceStr = NumStr33: }else if charset == "char"{34: sourceStr = CharStr35: }else if charset == "mix" {36: sourceStr = fmt.Sprintf("%s%s", NumStr, CharStr)37: }else if charset == "advance" {38: sourceStr = fmt.Sprintf("%s%s%s", NumStr, CharStr, SpecStr)39: }else {40: sourceStr = NumStr41: }42: fmt.Println("sourceStr:", sourceStr)43: for i:=0;i<length;i++{44: index := rand.Intn(len(sourceStr))45: password[i] = sourceStr[index]46: }47: return string(password)48: }49: func main() {50: rand.Seed(time.Now().UnixNano())51: parseArgs()52: fmt.Printf("length:%d charset:%s\n", length, charset)53: passwd := generatePasswd()54: fmt.Println(passwd)55: }
編譯後輸入：
1: main.exe -l 45 -t num
結果
1: length:45 charset:num2: sourceStr: 01234567893: 263415358329572320363459838031515468782761014
Go語言學習筆記(十)之切片