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Zhang_derek

第三章、Go-内建容器

3.1.数组

(1)数组的定义

package main

import (
	"fmt"
)

func main() {
	//用var定义数组可以不用赋初值
	var arr1 [5]int                  //[0 0 0 0 0]
	//用冒号必须指定初值
	arr2 := [3]int{1,3,5}            //[1 3 5]
	//用“...”表示任意个数
	arr3 := [...]int{2,4,6,8,10}     //[2 4 6 8 10]
	fmt.Println(arr1,arr2,arr3)
}

(2)数组的遍历

用range关键字

package main

import (
	"fmt"
)

func main() {
	arr3 := [...]int{2,4,6,8,10}     //[2 4 6 8 10]
	fmt.Println(arr3)

	//数组的遍历
	for i := range arr3{
		fmt.Println(arr3[i])
	}
}


//结果
2
4
6
8
10

获取下标和值

package main

import (
	"fmt"
)

func main() {
	arr3 := [...]int{2,4,6,8,10}     //[2 4 6 8 10]
	fmt.Println(arr3)

	//数组的遍历
	for i ,v:= range arr3{
		fmt.Println(i,v)
	}
}

//结果
0 2
1 4
2 6
3 8
4 10

(3)数组是值类型

  • [10]int和[20]int是不同类型
  • 调用func f(arr [10]int) 会拷贝数组
  • 在go语言中一般不使用数组,而使用切片
package main

import (
	"fmt"
)

func printArray(arr [5]int){
	for i ,v:= range arr{
		fmt.Println(i,v)
	}
}

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


//结果
0 2
1 4
2 6
3 8
4 10

 如果传arr2则报错

package main

import (
	"fmt"
)

func printArray(arr [5]int){
	for i ,v:= range arr{
		fmt.Println(i,v)
	}
}

func main() {
	arr2 := [3]int{1,3,5}
	//arr3 := [...]int{2,4,6,8,10}
	printArray(arr2)     //cannot use arr2 (type [3]int) as type [5]int in argument to printArray
}

3.2.切片

(1)切片

package main

import "fmt"

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

(2)slice的扩展

slice可以向后扩展,不可以向前扩展

package main

import "fmt"

func main() {
	arr := [...]int{0,1,2,3,4,5,6,7}
	s1 := arr[2:6]
	s2 := s1[3:5]
	fmt.Println(s1)     //[2 3 4 5]
	fmt.Println(s2)    //[5 6]
}

 s2是如何取到[5,6]的

 

 (3)slice的实现

 slice底层隐藏了三个值

s[i]不可以超越len(s),向后扩展不可以超越底层数组cap(s)

package main

import "fmt"

func main() {
	arr := [...]int{0,1,2,3,4,5,6,7}
	s1 := arr[2:6]
	s2 := s1[3:5]
	fmt.Println("arr = ",arr)                                         //arr =  [0 1 2 3 4 5 6 7]
	fmt.Printf("s1=%v,len(s1)=%d,cap(s1)=%d\n",s1,len(s1),cap(s1))   //s1=[2 3 4 5],len(s1)=4,cap(s1)=6
	fmt.Printf("s2=%v,len(s2)=%d,cap(s2)=%d\n",s2,len(s2),cap(s2))   //s2=[5 6],len(s2)=2,cap(s2)=3
	fmt.Println(s1[3:6])                                             //[5 6 7]
}

3.3.切片的操作

(1)向slice添加元素

  • 添加元素时,如果超出了cap,系统会重新分配更大的底层数组
  • 由于值传递的关系,必须接收append的返回值。s = append(s,val)
package main

import "fmt"

func main() {
	arr := [...]int{0,1,2,3,4,5,6,7}
	s1 := arr[2:6]         //[2 3 4 5]
	s2 := s1[3:5]          //[5 6]
	s3 := append(s2,10)
	s4 := append(s3,11)
	s5 := append(s4,12)
	fmt.Println(s3,s4,s5)    //[5 6 10] [5 6 10 11] [5 6 10 11 12]
	//因为s2的cap是[5,6,7],s3 append把7替换成10,s4后超出了cap
	fmt.Println(arr)         //[0 1 2 3 4 5 6 10]
}

(2)slice的创建

package main

import "fmt"

func main() {
	//第一种
	//Zero value for slice is nil
	var s1 []int
	fmt.Println(s1)    //[]

	for i := 0; i < 5 ; i++{
		s1 = append(s1,i)
	}
	fmt.Println(s1)    //[0 1 2 3 4]

	//第二种
	s2 := []int{2,4,6,8}
	fmt.Printf("len(s2)=%d,cap(s2)=%d\n",len(s2),cap(s2))    //len(s2)=4,cap(s2)=4

	//第三种
	s3 := make([]int,16)
	fmt.Printf("len(s3)=%d,cap(s3)=%d\n",len(s3),cap(s3))    //len(s3)=16,cap(s3)=16

	//第四种
	s4 := make([]int,16,32)
	fmt.Printf("len(s4)=%d,cap(s4)=%d\n",len(s4),cap(s4))    //len(s4)=16,cap(s4)=32
}

(3)slice的删除

package main

import "fmt"

func main() {
	s1 := []int{0,1,2,3,4,5,6}
	fmt.Println(s1)                   //[0 1 2 3 4 5 6]
	//删除index为3的值
	s1 = append(s1[:3],s1[4:]...)
	fmt.Println(s1)                   //[0 1 2 4 5 6]
}

3.4.Map  

(1)map的三种建立方式

package main

import "fmt"

func main() {
	//第一种
	m1 := map[string]string{
		"name":   "derek",
		"course": "go",
		"city":   "guangdong",
	}
	fmt.Println(m1)         //map[city:guangdong course:go name:derek]

	//第二种
	m2 := make(map[string]int)
	fmt.Println(m2)          //map[]

	//第三种
	var m3 map[string]string
	fmt.Println(m3)           //map[]
}

(2)map的遍历

package main

import "fmt"

func main() {
	m1 := map[string]string{
		"name":   "derek",
		"course": "go",
		"city":   "guangdong",
	}
	fmt.Println(m1)         //map[city:guangdong course:go name:derek]

	for k,v := range m1{
		fmt.Println(k,v)
	}
}

//结果
name derek
course go
city guangdong

(3)值的获取

key存在获取,不存在则得到空值

package main

import "fmt"

func main() {
	m1 := map[string]string{
		"name":   "derek",
		"course": "go",
		"city":   "guangdong",
	}
	fmt.Println(m1)         //map[city:guangdong course:go name:derek]

	//获取map中key的value
	courseName := m1["course"]
	fmt.Println(courseName)    //go

	//如果key不存在,不会报错,而是得到一个空值
	age := m1["age"]
	fmt.Println(age)    //空值
}

(4)用if判断取值

package main

import "fmt"

func main() {
	m1 := map[string]string{
		"name":   "derek",
		"course": "go",
		"city":   "guangdong",
	}
	fmt.Println(m1)         //map[city:guangdong course:go name:derek]

	//key存在,ok = true
	courseName,ok := m1["course"]
	fmt.Println(courseName, ok)    //go true

	//key不存在,ok = false
	age, ok := m1["age"]     // ok = false
	fmt.Println(age,ok)

	//取值的时候加一个判断,ok=true取值,否则打印值不存在
	if age, ok := m1["age"]; ok{
		fmt.Println(age)
	}else {
		fmt.Println("key does not exist")
	}
}

(5)删除key

package main

import "fmt"

func main() {
	m1 := map[string]string{
		"name":   "derek",
		"course": "go",
		"city":   "guangdong",
	}
	fmt.Println(m1)         //map[city:guangdong course:go name:derek]
	
	//删除key
	delete(m1,"city")
	fmt.Println(m1)         //map[course:go name:derek]

}

  

posted on 2019-08-02 00:02  zhang_derek  阅读(267)  评论(0编辑  收藏  举报

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