为什么我的代码中出现分段错误（核心转储）错误？

Question

此代码用于使用邻接表创建图形。
node是垂直链表每个元素的水平链表结构，
而graphnode是垂直链表的结构。

代码编译正确，但是当给出第一个输入时，它在它之后显示分段错误。

#include<iostream>
using namespace std;
struct node        //struct
{
    struct node *next;
    char value;
};
struct graphnode
{
    struct node *start;
    struct graphnode *down;
    char value;
    int count;
};
graphnode * creategraphnode(char val)
{
    struct graphnode *newnode=new graphnode;
    newnode->start=NULL;
    newnode->down=NULL;
    newnode->value=val;
    newnode->count=0;
    return newnode;
}
node *createnode(char val)
{
    struct node *newnode=new node;
    newnode->next=NULL;
    newnode->value=val;
}
void insertgraphnode(char value,graphnode *graph)
{
    struct graphnode *newnode=creategraphnode(value);
    if(graph==NULL)
    {
        graph=newnode;
    }
    else
    {
        graphnode *temp=graph;
        while(temp->down)
            temp=temp->down;
        temp->down=newnode;
    }
}
void insertnode(graphnode *graph)
{
    char val;
    struct node *temp=graph->start;
    cout<<"What is the outdegree of "<<graph->value;
    cin>>graph->count;
    cout<<"\nEnter"<<graph->count<<" nodes separated by space:";
    for(int i=1;i<=graph->count;i++)
    {
        cin>>val;
        node* newnode=createnode(val);
        temp=newnode;
        temp=temp->next;
    }
}
void display(struct graphnode *graph)
{
    if(graph==NULL)
    {
        cout<<"\nNo data to display";
        return;
    }
    struct graphnode *temp=graph;
    while(temp)
    {
        struct node *temp1=temp->start;
        cout<<temp->value<<"=>> ";
        if(temp1==NULL)
        {
            continue;
        }
        else
        {
            while(temp1)
            {
                cout<<temp1->value<<"-> ";
                temp1=temp1->next;
            }
        }
        cout<<"/\n";
    }
}
int main()
{
    struct graphnode *graph=NULL;
    int totalnodes;
    char val;
    cout<<"\nHow many nodes does the graph contain? : ";
    cin>>totalnodes;
    cout<<"\nEnter "<<totalnodes<<" space separated nodes : ";
    for(int i=1;i<=totalnodes;i++)
    {
        cin>>val;
        insertgraphnode(val,graph);
    }
    struct graphnode *temp=graph;
    while(temp->down)
    {
        insertnode(temp);
        temp=temp->down;
    }
    display(graph);
    return 0;
}

Answer 1

如果我没记错的话，你的代码至少有三个问题。

1）您的createnode()不返回创建的节点； 添加return newnode;

2）您的insertgraphnode()不更改调用函数中的第二个参数； 所以，当你在main()调用它时

insertgraphnode(val,graph);

graph NULL ； 在insertgraphnode()内更改值但在函数graph保持NULL ； 曾经。 这会导致分段错误。

您可以解决这个不断变化的insertgraphnode()因此第二个参数是一个指向指针的指针并传递&graph 。

另一种解决方案是修改insertgraphnode()以返回graph值

graphnode *  insertgraphnode(char value,graphnode *graph)
{
    struct graphnode *newnode=creategraphnode(value);
    if(graph==NULL)
    {
        graph=newnode;
    }
    else
    {
        graphnode *temp=graph;
        while(temp->down)
            temp=temp->down;
        temp->down=newnode;
    }
    return graph;
}

并以这种方式调用它

graph = insertgraphnode(val,graph);

3） while在display()去中环，因为你不改变的值temp