Go language slice vs array panic: runtime error: index out of range problem solving

Beginners Go An array of languages （array） Type and slice （slice） type , I am confused about these two concepts , I don't know how to use it ？ When to use array or slice

Catalog

Preface

One 、go slice What is it?

Two 、go slice Practical cases

1.slice establish 、 Use

2、slice Understand the concept of length and capacity

3. Slice expansion and slice panic: runtime error: index out of range

summary

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Preface

stay go In the course of language learning ,slice The data type aroused my curiosity . Why not just use it Slice, Is the distortion of human nature or moral collapse ~, Let's take a look at ~~

One 、go slice What is it?

go In language slice It's based on Array Encapsulated data structure ,go In language slice The frequency of use is much higher than array, Its figure frequently appears in the source code implementation .slice be relative to Array Its advantage is that it can dynamically adjust its own size, Unlike Array Of Size Is constant .

Two 、go slice Practical cases

1.slice establish 、 Use

slice There are two ways to create a. S. are using literal definitions and using make function . Excepting slice establish , other slice The generation methods of are all from the existing slice Slice or array Do on slice Shard operation .

slice Create code ：

package main

import (
	"fmt"
	"reflect"
)

func main() {
	// Literal creation Slice
	sliceOne := []string{"a", "b"}
	// Use make Function creation slice
	sliceTwo := make([]string, 10)
	sliceThree := make([]int, 10)

	fmt.Printf(" Created with literal slice%s\n",reflect.ValueOf(sliceOne).String())
	fmt.Printf(" Use make Function created slice:%s\n",reflect.ValueOf(sliceTwo).String())
	fmt.Printf(" Use make Function created slice:%s\n",reflect.ValueOf(sliceThree).String())

}

Program output ：

 Created with literal slice<[]string Value>
 Use make Function created slice:<[]string Value>
 Use make Function created slice:<[]int Value>

Process finished with the exit code 0

2、slice Understand the concept of length and capacity

Learning process , A lot of kids will be right slice There is a lot of confusion about the length and capacity of .

This place can be compared to a place that can hold 10 An apple bag , There are three apples in the bag now . The length of the slice is the number of fruits in the bag , At present, it is 3 individual . The capacity of slicing is the total number of fruits in this bag , For this bag, it is 10. Then replace the code with slices , Replace the apple with the element , Is it right that I understand the meaning of Sa ~

The following is how to deal with this problem, which is to go directly to the official , Look at the source code . Look at the first-hand information ！

 

 length ：slice Number of elements in , If slice yes nil Words , Then the length of the number of elements is 0
 english ：the number of elements in v; if v is nil, len(v) is zero

 Capacity ：slice The maximum length of the slice that can be reached 
 english ：Slice: the maximum length the slice can reach when resliced;

Code verification ：

package main

import (
	"fmt"
 )

func main() {
	sliceOne := []string{"a", "b"}
	strings := sliceOne[0:1]
	fmt.Printf(" The length of the slice :%d\n",len(strings))
	fmt.Printf(" The volume of the slice :%d\n",cap(strings))
}

Code result output ：

 The length of the slice :1
 The volume of the slice :2

Code principle analysis ：

strings from sliceOne Sliced , There are a lot of on-chip data cut out 0 To 1, There's an element , So the corresponding length is 1.

Because slice is a reference type , Only on the original slice 0 To 1 The location of , There are still... Vacant seats left 1, Therefore, its capacity is equal to the length plus the number of remaining element positions .

3. Slice expansion and slice panic: runtime error: index out of range

slice Examples of out of bounds code are as follows ：

	sliceOne := []string{"a", "b"}
	// Use make Function creation slice
	s := sliceOne[2]
	fmt.Printf(s)

Use sliceOne[2] When the sentence is , Array out of bounds error .

In the actual development process , There will always be slice When the capacity is not enough , How to expand the capacity , How to ensure safe expansion ？

go The expansion method provided by the language official is to create a new and larger partition , Migrate the data content of the old slice to the new slice .

Code display ：

package main

import (
	"fmt"
 )

func main() {
	sliceOne := []string{"a", "b"}
	fmt.Printf(" Before slice expansion ")
	fmt.Printf(" The length of the slice :%d\n",len(sliceOne))
	fmt.Printf(" The volume of the slice :%d\n",cap(sliceOne))
	t := make([]string, len(sliceOne), (cap(sliceOne))*2)
	copy(t, sliceOne)
	sliceOne = t
	fmt.Printf(" After slicing and volume expansion ")
	fmt.Printf(" The length of the slice :%d\n",len(sliceOne))
	fmt.Printf(" The volume of the slice :%d\n",cap(sliceOne))
}

Result display ：

 The length of the slice :2
 The volume of the slice :2
 The length of the slice :2
 The volume of the slice :4

  From the code result, we can see that the length of the new slice is 2, Capacity is 4, It is also verified that the length of the slice depends on how many elements are stored , The capacity of the slice depends on the number of elements stored plus the number of remaining positions .

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summary

go In language slice The application and use of is relatively convenient and fast , But there are also some small dark pits waiting to be discovered and sorted out ~ In the future, I will write in my blog , Continue to post about go Used in language tips And skills ~

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