go的slice拷贝,修改,append

package main

import (
	"fmt"
)

func testMake1() {
	var a []int
	//a = make([]int, 1, 10) // 切片如果直接使用a = append(a, 11)可以不初始化, 直接a[0] = 10这样赋值,必须初始化
	fmt.Printf("00 a=%v\n", a)
	fmt.Printf("00 a=%v addr:%p len:%d cap:%d  \n", a, a, len(a), cap(a))
	//a[0] = 10
	fmt.Printf("01 a=%v\n", a)
	// a[1] =20
	a = append(a, 11)
	fmt.Printf("02 a=%v\n", a)
	fmt.Printf("03 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("04 a=%v addr:%p len:%d cap:%d  \n", a, a, len(a), cap(a))
	}
	a = append(a, 100)
	fmt.Printf("05 扩容之后的地址  a=%v addr:%p len:%d cap:%d  \n", a, a, len(a), cap(a))
}

func testMake2() {
	var a []int
	a = make([]int, 5, 10)
	a = append(a, 10)
	fmt.Printf("a=%v \n", a)

	b := make([]int, 0, 10)
	fmt.Printf("00>>b=%v len:%d cap:%d\n", b, len(b), cap(b))
	b = append(a, 100)
	fmt.Printf("01>>b=%v len:%d cap:%d\n", b, len(b), cap(b))
}



func testCap() {
	a := [...]string{"a", "b", "c", "d", "e", "f", "g", "h"}
	b := a[1:3]
	fmt.Printf("b=%v len:%d cap:%d\n", b, len(b), cap(b))
	b = b[:cap(b)]
	fmt.Printf("after reslice>> b:%v len:%d cap:%d\n", b, len(b), cap(b))
}

func testSlice() {
	var a []int
	fmt.Printf("addr(a)=%p,  len:%d,  cap:%d\n", a, len(a), cap(a))

	if a == nil {
		fmt.Printf("a is nil\n")
	}
	a = append(a, 100)
	fmt.Printf("%p,   len:%d cap:%d\n", a, len(a), cap(a))
	a = append(a, 200)
	fmt.Printf("%p,   len:%d cap:%d\n", a, len(a), cap(a))
	a = append(a, 301)
	fmt.Printf("%p,   len:%d cap:%d\n", a, len(a), cap(a))
	a = append(a, 401)
	fmt.Printf("%p,   len:%d cap:%d\n", a, len(a), cap(a))
	a = append(a, 501)
	fmt.Printf("%p,   len:%d cap:%d\n", a, len(a), cap(a))
}

func testAppend() {
	var a []int = []int{1, 3, 4}
	fmt.Printf("01  a:%v \n", a)
	var b []int = []int{4, 5, 6}

	a = append(a, 23, 34, 45)
	fmt.Printf("02  a:%v \n", a)

	c := append(a, b...) // 切片后面加...把切片展开

	fmt.Printf("03  a:%v \n", a)
	fmt.Printf("03  b:%v \n", b)
	fmt.Printf("03  c:%v \n", c)
}

func sumArray(a []int) int {
	var sum int = 0
	for _, v := range a {
		sum = sum + v
	}
	return sum
}

func testSumArray() {
	var a [10]int = [10]int{1, 2, 3, 4, 5,  6, 7, 8, 9}
	fmt.Printf("Array(a)>>%#v, Slice(a)>>%#v \n", a,a[:])
	sum := sumArray(a[:])
	fmt.Println("sum>>a:", sum)
}

func modifySlice(a []int) {
	a[0] = 100
}

func testModifyCopy() {
	var a []int = []int{1, 2, 3, 7, 8, 9, 8, 99}
	var b []int = []int{4, 5, 6, 66}
	copy(a, b)  // 把b中的拷贝到a中去
	fmt.Println("a", a)
	fmt.Println("b", b)
	fmt.Printf("a的类型%T\n", a)
	fmt.Printf("b的类型%T\n", b)
}

func testModifySlice() {
	var a [3]int = [3]int{1, 2, 3}
	fmt.Println("modify before",a)
	modifySlice(a[:])
	fmt.Println("modify after",a)
}

func main() {
	//testMake1()
	//testMake2()
	//testCap()
	//testSlice()
	testAppend()
	testSumArray()
	testModifySlice()
	testModifyCopy()
}

案例二:

package main

import(
	"fmt"	
)


func main(){	
	var a []string = make([]string,5,10)
	fmt.Println("a",a)
	for i:=0;i<10;i++{
		a=append(a,fmt.Sprintf("%d",i))
	}
	fmt.Printf("a:%v %d %d",a,len(a),cap(a))
}

切记: 用make(make([]string,5,10))初始化切片时,直接生成了一个切片,他的前5个元素是'',长度为5, 容量10,往他里面添加元素请用a[i],而不是append
输出:

a [    ]
a:[     0 1 2 3 4 5 6 7 8 9] 15 20