go - panic : runtime error: invalid memory address or nil pointer dereference [signal 0xc0000005 code=0x0 addr=0x8 pc=0x48be5c] goroutine 1 [running]:

Question

我正在尝试使用链表实现多项式的加法。该程序成功地添加了幂 0 系数，但在第一次遍历后它出现了困惑。这是我到目前为止编写的代码。在初始化 temp1!= nil 之后，循环遍历 else 但当权力不同时不进入 if 循环并进入 panic 状态

package main

import (
    "fmt"
)

type Node struct {
    coefficient int
    power       int
    next        *Node
}

type list struct {
    head  *Node
    count int
}

func main() {
    list1 := &list{}
    list1.addVariable(5, 2)
    list1.addVariable(4, 1)
    list1.addVariable(3, 0)
    list1.print()
    list2 := &list{}
    list2.addVariable(4, 1)
    list2.addVariable(2, 0)
    list2.print()
    list4 := addLists(list1, list2)
    list4.print()

}

func (lst *list) print() {
    temp := lst.head
    for temp != nil {
        fmt.Print(temp.coefficient, "x", "^", temp.power, "+")
        temp = temp.next
    }
    fmt.Println("\n")
}

func (lst *list) addVariable(coefficient int, power int) {
    lst.head = &Node{coefficient, power, lst.head}
    lst.count++
}

func addLists(list1 *list, list2 *list) *list {
    list3 := &list{}
    temp1 := list1.head
    temp2 := list2.head
    fmt.Println("reached") // for debugging purposes
    if list1.count > list2.count {
        fmt.Println("\nreached 2") // for debugging purposes
        for temp1 != nil {
            fmt.Println("reached3") // for debugging purposes
            if temp1.power != temp2.power {
                fmt.Println("reached4") // for debugging purposes
                list3.normalAdd(temp1, temp2)
                temp1 = temp1.next

            } else {
                fmt.Println("reached5") // for debugging purposes
                node4 := add(temp1, temp2)
                list3.exlusiveAdd(node4)
                temp1 = temp1.next
                temp2 = temp2.next
            }
        }
    }
    return list3
}

func (lst *list) normalAdd(node6 *Node, node7 *Node) {
    node6.next = lst.head
    lst.head = node6
    node7.next = lst.head
    lst.head = node7
    lst.count += 2
}

func (lst *list) exlusiveAdd(node5 *Node) {
    node5.next = lst.head
    lst.head = node5
    lst.count++
}

func add(node1, node2 *Node) *Node {
    node3 := &Node{}
    node3.coefficient = node1.coefficient + node2.coefficient
    node3.power = node1.power
    return node3
}

程序运行时的输出:

3x^0+4x^1+5x^2+
2x^0+4x^1+
reached

reached 2
reached3
reached5
reached3
reached5
reached3
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0xffffffff addr=0x0 pc=0xd48e6]

goroutine 1 [running]:
main.addLists(0x41c7a8, 0x41c7a0, 0x40c120, 0x1d)
    /tmp/sandbox520212269/main.go:56 +0x186
main.main()
    /tmp/sandbox520212269/main.go:28 +0x220

Playground here

更新:感谢您的解决方案，但我已经成功编写了上述问题的代码。这里是。 包主

import (
"fmt"
)

type Node struct {
coefficient int
power       int
next        *Node
}

type list struct {
head  *Node
count int
}

func main() {
list1 := &list{}
list1.addVariable(5, 2)
list1.addVariable(4, 1)
list1.addVariable(3, 0)
list1.print()
list2 := &list{}
list2.addVariable(4, 1)
list2.addVariable(2, 0)
list2.print()
poly := addPoly(list1, list2)
poly.print()
}

func (lst *list) print() {
temp := lst.head
for temp != nil {
    fmt.Print(temp.coefficient, "x", "^", temp.power, "+")
    temp = temp.next
}
fmt.Println("\n")
}

func (lst *list) addVariable(coefficient int, power int) {
lst.head = &Node{coefficient, power, lst.head}
lst.count++
}

func addPoly(list_1 *list, list_2 *list) *list {
list_3 := &list{}
temp_1 := list_1.head
temp_2 := list_2.head
if list_1.count > list_2.count {
    for temp_1 != nil && temp_2 != nil {
        if temp_1.power == temp_2.power {
            new_coefficient := temp_1.coefficient + temp_2.coefficient
            new_power := temp_1.power
            list_3.addVariable(new_coefficient, new_power)
            temp_1 = temp_1.next
            temp_2 = temp_2.next
        } else if temp_1.power != temp_2.power {
            list_3.addVariable(temp_1.coefficient, temp_1.power)
            list_3.addVariable(temp_2.coefficient, temp_2.power)
            temp_1 = temp_1.next
            temp_2 = temp_2.next
        }
    }
}
for temp_1 != nil {
    list_3.addVariable(temp_1.coefficient, temp_1.power)
    temp_1 = temp_1.next
}
return list_3
}

Answer 1

错误发生是因为您试图在下面的代码中从 nil 对象访问 .power 属性。 temp1 和 temp2 都是 nil。

if temp1.power != temp2.power {
   // ...
}

list 结构上的.head 属性具有指针数据类型。指针数据类型的零值是nil。在您的代码中，list1 和 list2 的 .head 属性都具有 nil 值。

您需要做的:在创建 list1 和 list2 期间明确初始化 .head 属性的值。然后 panic 错误将消失，您的代码将正常工作。

list1 := &list{head: new(Node)}
// ...
list2 := &list{head: new(Node)}
// ...

Playground :https://play.golang.org/p/vPK3pYKht3E