golang 數組 切片 Map rune

一、數組

package main

import "fmt"

func printArray(arr [5]int) {//無法改變原值
	arr[0] = 100
	for i, v := range arr { //遍歷數組
		fmt.Println(i, v)
	}
}

func main() {
	var arr1 [5]int
	arr2 := [3]int{1, 3, 5}
	arr3 := [...]int{2, 4, 6, 8, 10}
	var grid [4][5]int

	fmt.Println("array definitions:")
	fmt.Println(arr1, arr2, arr3)
	fmt.Println(grid)

	fmt.Println("printArray(arr1)")
	printArray(arr1)

	fmt.Println("printArray(arr3)")
	printArray(arr3)

	fmt.Println("arr1 and arr3")
	fmt.Println(arr1, arr3)
}

二、Slice

package main

import "fmt"

func updateSlice(s []int) {//能夠改變原值
	s[0] = 100
}

func main() {
	arr := [...]int{0, 1, 2, 3, 4, 5, 6, 7}

	fmt.Println("arr[2:6] =", arr[2:6])
	fmt.Println("arr[:6] =", arr[:6])
	s1 := arr[2:]
	fmt.Println("s1 =", s1)
	s2 := arr[:]
	fmt.Println("s2 =", s2)

	fmt.Println("After updateSlice(s1)")
	updateSlice(s1)
	fmt.Println(s1)
	fmt.Println(arr)

	fmt.Println("After updateSlice(s2)")
	updateSlice(s2)
	fmt.Println(s2)
	fmt.Println(arr)

	fmt.Println("Reslice")
	fmt.Println(s2)
	s2 = s2[:5]
	fmt.Println(s2)
	s2 = s2[2:]
	fmt.Println(s2)

	fmt.Println("Extending slice")
	arr[0], arr[2] = 0, 2
	fmt.Println("arr =", arr)
	s1 = arr[2:6]
	s2 = s1[3:5] // [s1[3], s1[4]]
	fmt.Printf("s1=%v, len(s1)=%d, cap(s1)=%d\n",
		s1, len(s1), cap(s1))
	fmt.Printf("s2=%v, len(s2)=%d, cap(s2)=%d\n",
		s2, len(s2), cap(s2))

	s3 := append(s2, 10)//修改了原數組的值
	s4 := append(s3, 11)//新切片，不修改原數組的值
	s5 := append(s4, 12)//新切片，不修改原數組的值
	fmt.Println("s3, s4, s5 =", s3, s4, s5)
	// s4 and s5 no longer view arr.
	fmt.Println("arr =", arr)

	// Uncomment to run sliceOps demo.
	// If we see undefined: sliceOps
	// please try go run slices.go sliceops.go
	fmt.Println("Uncomment to see sliceOps demo")
	// sliceOps()
}

輸出：

arr[2:6] = [2 3 4 5]
arr[:6] = [0 1 2 3 4 5]
s1 = [2 3 4 5 6 7]
s2 = [0 1 2 3 4 5 6 7]
After updateSlice(s1)
[100 3 4 5 6 7]
[0 1 100 3 4 5 6 7]
After updateSlice(s2)
[100 1 100 3 4 5 6 7]
[100 1 100 3 4 5 6 7]
Reslice
[100 1 100 3 4 5 6 7]
[100 1 100 3 4]
[100 3 4]
Extending slice
arr = [0 1 2 3 4 5 6 7]
s1=[2 3 4 5], len(s1)=4, cap(s1)=6
s2=[5 6], len(s2)=2, cap(s2)=3
s3, s4, s5 = [5 6 10] [5 6 10 11] [5 6 10 11 12]
arr = [0 1 2 3 4 5 6 10]

 

切片是對數組的view，可以修改數組原值，len是當前取值範圍大小，cap是實際的數組大小。

s1：len(s1)=4, cap(s1)=6，s2 = s1[3:5]取的cap範圍的數據。

三、Slice的操作

package main

import "fmt"

func printSlice(s []int) {
	fmt.Printf("%v, len=%d, cap=%d\n",
		s, len(s), cap(s))
}

func sliceOps() {
	fmt.Println("Creating slice")
	var s []int // Zero value for slice is nil

	for i := 0; i < 100; i++ {
		printSlice(s)
		s = append(s, 2*i+1)//len和cap不斷擴大，cap一般會比len大些，且是2的n次方
	}
	fmt.Println(s)

	s1 := []int{2, 4, 6, 8}
	printSlice(s1)

	s2 := make([]int, 16)
	s3 := make([]int, 10, 32)
	printSlice(s2)
	printSlice(s3)

	fmt.Println("Copying slice")
	copy(s2, s1)
	printSlice(s2)

	fmt.Println("Deleting elements from slice")
	s2 = append(s2[:3], s2[4:]...)
	printSlice(s2)

	fmt.Println("Popping from front")
	front := s2[0]
	s2 = s2[1:]

	fmt.Println(front)
	printSlice(s2)

	fmt.Println("Popping from back")
	tail := s2[len(s2)-1]
	s2 = s2[:len(s2)-1]

	fmt.Println(tail)
	printSlice(s2)
}

輸出：

len=0, cap=0
len=1, cap=1
len=2, cap=2
len=3, cap=4
len=4, cap=4
len=5, cap=8
len=6, cap=8
len=7, cap=8
len=8, cap=8
len=9, cap=16
len=10, cap=16
len=11, cap=16
len=12, cap=16
len=13, cap=16
len=14, cap=16
len=15, cap=16
len=16, cap=16
len=17, cap=32
len=18, cap=32
len=19, cap=32
len=20, cap=32
[2 4 6 8], len=4, cap=4
[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0], len=16, cap=16
[0 0 0 0 0 0 0 0 0 0], len=10, cap=32
Copying slice
[2 4 6 8 0 0 0 0 0 0 0 0 0 0 0 0], len=16, cap=16
Deleting elements from slice
[2 4 6 0 0 0 0 0 0 0 0 0 0 0 0], len=15, cap=16
Popping from front
2
[4 6 0 0 0 0 0 0 0 0 0 0 0 0], len=14, cap=15
Popping from back
0
[4 6 0 0 0 0 0 0 0 0 0 0 0], len=13, cap=15

四、Map

package main

import "fmt"

func main() {
	m := map[string]string{
		"name":    "ccmouse",
		"course":  "golang",
		"site":    "imooc",
		"quality": "notbad",
	}

	m2 := make(map[string]int) // m2 == empty map

	var m3 map[string]int // m3 == nil

	fmt.Println("m, m2, m3:")
	fmt.Println(m, m2, m3)

	fmt.Println("Traversing map m")
	for k, v := range m {
		fmt.Println(k, v)
	}

	fmt.Println("Getting values")
	courseName := m["course"]
	fmt.Println(`m["course"] =`, courseName)
	if causeName, ok := m["cause"]; ok {
		fmt.Println(causeName)
	} else {
		fmt.Println("key 'cause' does not exist")
	}

	fmt.Println("Deleting values")
	name, ok := m["name"]
	fmt.Printf("m[%q] before delete: %q, %v\n",
		"name", name, ok)

	delete(m, "name")
	name, ok = m["name"]
	fmt.Printf("m[%q] after delete: %q, %v\n",
		"name", name, ok)
}

輸出：

m, m2, m3:
map[course:golang name:ccmouse quality:notbad site:imooc] map[] map[]
Traversing map m
name ccmouse
course golang
site imooc
quality notbad
Getting values
m["course"] = golang
key 'cause' does not exist
Deleting values
m["name"] before delete: "ccmouse", true
m["name"] after delete: "", false

五、string

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	s := "Yes我愛中國!" // UTF-8
	fmt.Println(s)

	for _, b := range []byte(s) {//按字節
		fmt.Printf("%X ", b)
	}
	fmt.Println()

	for i, ch := range s { // ch is a rune
		fmt.Printf("(%d %X) ", i, ch)
	}
	fmt.Println()

	fmt.Println("Rune count:",
		utf8.RuneCountInString(s))

	bytes := []byte(s)
	for len(bytes) > 0 {
		ch, size := utf8.DecodeRune(bytes)
		bytes = bytes[size:]
		fmt.Printf("%c ", ch)
	}
	fmt.Println()

	for i, ch := range []rune(s) {
		fmt.Printf("(%d %c) ", i, ch)
	}
	fmt.Println()
}

輸出：

Yes我愛中國!
59 65 73 (E6 88 91) (E7 88 B1) (E4 B8 AD) (E5 9B BD) 21 
(0 59) (1 65) (2 73) (3 6211) (6 7231) (9 4E2D) (12 56FD) (15 21) 
Rune count: 8
Y e s 我 愛 中 國 ! 
(0 Y) (1 e) (2 s) (3 我) (4 愛) (5 中) (6 國) (7 !) 

type byte = uint8

// rune is an alias for int32 and is equivalent to int32 in all ways. It is
// used, by convention, to distinguish character values from integer values.
type rune = int32

在上面的例子中中文佔3個字節，英文佔1個字節。

https://learnku.com/articles/23411/the-difference-between-rune-and-byte-of-go 

rune和byte的區別這篇文章講的很清楚。