Go language 4-arrays, slices, and maps

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1. Arrays
Array length definition cannot be modified, the number of array elements is obtained through the built-in function Len ()

1）类型

    //长度为32的byte数组，每个元素为一个字节    [32]byte    //长度为2*N的复杂类型数组    [2structint32}    //长度100的指针数组    [100]*float64    //二维数组，等同于[2]([3]int)    [2][3]int    //三维数组    [2][2][2]float64

2）定义

    //Defines an array of length 5, which is initialized by default with 0 values of type int (0)Arr: =[5]int{}//As in the above sentence    varArr[5]int=[5]int{}//define an array of length 5, where arr[0] will be initialized to 1 and the rest is still 0Arr: =[5]int{1}//define an array of length 5, where arr[0], arr[4] will be initialized to 1, and the rest is still 0Arr: =[5]int{0: 1, 4: 1}//Defines an array of length 5, which is initialized by default with 0 values of type int (0)Arr: =New([5]int)//define and initialize an array, which automatically infers the length of the array ([...] ), this needs to be different from the definition of the following slices (no ...)Arr: = [...]int{1,2,3,4,5}//define and initialize an array, and will automatically infer that the length is 5,arr[4] will be initialized to 1, the rest is still 0Arr: = [...]int{4: 5}

3）遍历

 //and other programming language types traverse the way . Span class= "Hljs-comment" >//gets the length of the array arr  lenth: = len  (arr) 
   
    for  I: =
     0 ; i < lenth; i++ {
    //uses array indexing to traverse the array  fmt. Print (Arr[i], 
    )} //use range to iterate through the array, range has two return values, 1 is index, 2 is the value  for  i, V: = range  arr {fmt. Print ( "[" , I, "]=" , V, )} 
    

4）比较操作在两个数据是同一类型（长度及元素类型）时，可以使用==与!=对两个数组进行比较，但不能使用<或>。注：Go语言中数组是一个值类型，所有值类型变量在赋值和作为参数传递时都将产生一次复制动作，    传入函数中的数组仅是该数组的一个副本，因此就无法对其进行修改，如果此时的数组较大时，    将会降低程序的效率，关于这种场景的解决，下面的切片会进行讲解。

2. Slicing

在上面我们提到数组两个特点：1、数据长度在定义后无法再次进行修改；2、数据是值类型，每次传递都将产生一个副本；而Slice(切片)正是为解决以上两个问题而存在。从表象看，切片是一个指向原始数组的指针，但实际上，切片拥有自己的数据结构1、一个指向原生数组的指针2、数组切片中的元素个数3、数组切片已分配的存储空间这里需要区分两个概念，长度：切片已使用的大小，从切片头开始算起，使用内置函数len()获取容量：切片允许使用的大小，从切片头开始算起，至底层数组末尾，使用内置函数cap()获取，      当切片长度超过容量时，会重新分配一个原容量两倍的容间，并将值复制过去，与Java      中的ArrayList有点类似，要注意扩容后的内存地址与原内存地址不一样。1）定义

    //define an array here firstArr: =[5]int{}//Based on the data defined above, define a slice that points to the ARR index value in the [0,5] range (left open right)    //[M,n] here can also be written in several ways, such as [: 5] means [0,5], [1:] means [1,len (arr)], [:] means [0,len (arr) ]Arrslice: = arr[0: 5]//define a slice with a length of 5 and a capacity of 5, note that the difference between the definition of the above array and the definition of the array is in parentheses ...Arrslice: = []int{1, 2, 3, 4, 5}//define a slice with a length of 5 and a capacity of 5Myslice: = Make([]int, 5)//define a slice with a length of 5 and a capacity of 10Myslice: = Make([]int, 5, ten)//Slicing on slices, this is called Reslice, where [m:n] must meet 0<=m<n<=cap (Myslice)-MMySlice2: = myslice[:]

在reslice的情况下，有很多地方需要注意，因为原slice与reslice实际底层使用的是同一块内存空间，当两个的长度都在底层数组的长度内时，两者共享的都是同一块容间，当有一个超过之后，这种情况将会被打破。如下面的代码所示：

Myslice: = Make([]int, 5, 6)//i.e. myslice[1] corresponds to myslice2[1], etc.MySlice2: = Myslice[1:]//This is equivalent to also the value of myslice2[0] has been modifiedMyslice[1]  =Ten    //append is a built-in function that represents the append value to the slice, the myslice length is increased, but the mySlice2 length remains the same.Myslice =Append(Myslice, 1)//The value of myslice[5] will be overwritten with 2, that is, the value of the previous line of code is overwrittenMySlice2 =Append(MySlice2, 2)The space allocation will occur when you have exhausted all the space and added the value through the code aboveMySlice2 =Append(MySlice2,7)//This changes only myslice2[0], while myslice[1] does not changeMySlice2[0] =-1

2）遍历与数组遍历一样，这里就不复述了3）切片的增减

    //Add a value of 1 at the end of the slice and, if it exceeds the capacity, will result in a redistribution of the capacitance, which will be twice times the original capacityMyslice =Append(Myslice, 1)//Add multiple values at the end of the sliceMyslice =Append(Myslice, 1, 2, 3)//Append an array at the end of the slice, where the "..." is required, otherwise it compiles an error, which means that the array is broken and passed inMyslice =Append(Myslice,arr ...)//Add another slice at the end of the slice, where the MySlice2 [:] is omitted.Myslice =Append(Myslice,myslice2 ...)//Slice minus, this means delete myslice[1], the length of the slice decreases, but the capacity does not changeMyslice =Append(myslice[: 1],myslice[2:]...)//Slice minus, if you want to delete the end of the slice, you can use the Reslice method to implement theMyslice = Myslice[0:Len(Myslice)-1]

4）内容复制用于将内容从一个数组切片复制到另一个数组切片。如果两个切片不一样大，将以较小切片的元素个数进行复制

    //这里要注意顺序，与Java的那种前者from后者to相反    copy(targetSlice,sourceSlice)

3. Map
Unordered set of key-value pairs, built directly into the system without the need to introduce additional packages

1）声明var 变量名 map[键类型]值类型

    varmap[int]string

2）创建

    //Create a key of int, a value of string map,mymap need to be declared firstMyMap = Make(Map[int]string)//declaration + CreateMyMap: = Make(Map[int]string)//Create a map with a capacity of 100MyMap = Make(Map[int]string, the)//declaration + CreateMyMap =Map[int]string{}//declaration + Create + initializeMyMap =Map[int]string{1:"1"}

3）元素赋值、删除、查找

    //增加或修改key=123对应的元素值为字符型"123"    myMap[123"123"    //删除key=123对应的元素    delete(myMap,123)    //查找key=123对应的元素,该操作有两个返回值，多返回值知识点将在函数相关内容说到，    //返回值1为对应的值，返回值2为是否包含该key    v, ok := myMap[123]

This article introduces the two most commonly used data structures in programming, arrays and maps, and introduces a scalable "array" and can be seen as an array of pointers-slices, arrays and slices have too many similarities, but at the same time there are differences, so as a novice to pay special attention.

No smell (Unknow) "Go Programming Basics"
Xu Xiwei's "Go Language Programming"

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