In-depth introduction to the usage of golang slicing

[Introduction]

Go language is a C family programming language. It has the characteristics of efficiency, simplicity, safety, etc., and it also has some characteristics of modern programming languages. In the Go language, slice is a very important data type and is widely used in many situations. In this article, we will introduce the usage of slices in golang in depth to help everyone better understand the usage of slices in golang.

[1. Basic definition of slicing]

First, let us take a look at the basic definition of slicing in golang. In the Go language, a slice is a structure containing three fields: a pointer to an element of the array, length and capacity. When creating a slice, we need to use the built-in make() function, which has the following format:

func make([]T, len, cap) []T

Among them, T represents the element type of the slice, len represents the length of the slice, and cap represents the capacity of the slice. . When using the make() function, if the capacity is not specified, the capacity is equal to the length.

Specifically, we can create a slice through the following code:

a := make([]int, 5) //创建一个长度为5的int类型切片
b := make([]int, 3, 5) //创建一个长度为3，容量为5的int类型切片

As you can see, the make() function will return a new slice, which we can assign to a variable Perform operations.

[2. Basic operations of slicing]

After defining the slice, we can perform some basic operations on the slice. Below, we will introduce in detail the common operations of slicing in golang.

[2.1 Slice access and traversal]

First of all, we can access the elements in the slice through indexing. Like arrays, slice indexes in golang also start from 0. For example:

a := []int{1, 2, 3}
fmt.Println(a[0]) //输出1
fmt.Println(a[1]) //输出2
fmt.Println(a[2]) //输出3

At the same time, we can also use a for loop to traverse all the elements in the slice. For example:

a := []int{1, 2, 3}
for i:=0;i<len(a);i++ {
    fmt.Println(a[i])
}

In addition, golang also provides a range keyword, which we can use to traverse all elements in the slice. For example:

a := []int{1, 2, 3}
for i, v := range a {
    fmt.Println(i, v)
}

In the above code, i represents the index of the element, and v represents the value of the element.

[2.2 Slice append operation]

In golang, we can use the append() function to append new elements to the slice. This function has the following format:

func append(s []T, vs ...T) []T

where s represents the slice to be appended, and vs represents the element to be appended. In the append() function, we can pass one or more parameters and add them to the end of the slice. For example:

a := []int{1, 2, 3}
a = append(a, 4, 5, 6)
fmt.Println(a) //输出[1 2 3 4 5 6]

It should be noted that using the append() function will create a new slice. If the new slice needs to be assigned to a variable, then we need to reassign the variable, otherwise the original slice will not be changed.

[2.3 Slice copy operation]

In golang, we can use the copy() function to copy a slice. This function has the following format:

func copy(dst, src []T) int

where dst represents the target slice and src represents the source slice. When calling the copy() function, if the length of the target slice is smaller than the source slice, only the elements of the target slice length will be copied. For example:

a := []int{1, 2, 3}
b := make([]int, 2)
copy(b, a)
fmt.Println(b) //输出[1 2]

It should be noted that using the copy() function will also create a new slice.

[3. Slice expansion]

When appending elements to a slice, if the slice no longer has enough space, golang will automatically expand the slice. When expanding, golang will double the capacity of the slice and create a new underlying array. At the same time, golang will also copy the elements in the original slice to the new underlying array.

It should be noted that during expansion, if the length of the new underlying array is too long, golang will select the length of the new underlying array based on the number of elements in the current slice. Specifically, golang will make a selection based on the following rules:

• If the number of elements in the slice is less than 1024, the length of the new underlying array is equal to twice the original length;
• If If the number of elements in the slice is greater than or equal to 1024, the length of the new underlying array is equal to 1.25 times the original.

After understanding the expansion mechanism of slices in golang, we can make better use of slices and improve the efficiency of the program.

[4. Memory management of slices]

When using slices, we need to pay attention to memory management issues. In golang, the underlying slice corresponds to an array. When the slice is assigned to another variable, its underlying array will also be copied. For example:

a := []int{1, 2, 3}
b := a //将a赋值给b
b[0] = 4 //改变b中的第一个元素
fmt.Println(a) //输出[1 2 3]
fmt.Println(b) //输出[4 2 3]

It should be noted that if a slice is passed as a parameter to a function, since the underlying layer of the slice corresponds to an array, modifying the elements of the slice in the function will also affect the original slice. For example:

func changeSlice(a []int) {
    a[0] = 4 //修改a中的第一个元素
}

b := []int{1, 2, 3}
changeSlice(b)
fmt.Println(b) //输出[4 2 3]

After understanding the memory management issues of slicing and underlying arrays, we can better use slicing, improve program efficiency, and avoid unexpected effects on the underlying array.

[Conclusion]

Slice is a very important data type in golang and is widely used on many occasions. In this article, we introduce in detail the basic definition, operation, expansion and memory management of slices in golang. I hope this article can help you further understand the usage of slices in golang, so as to better use slices to develop efficient programs.

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