C++中的linkedlists運行時錯誤

Question

每當我運行此代碼以實現鏈接列表時，我都會遇到運行時錯誤。我認爲錯誤是在默認的構造函數中，因爲我試圖運行程序，其中只有對象沒有被創建。

的linkedlist.h文件

#ifndef LinkedList_h 
#define LinkedList_h 

#include<iostream> 
#include<string> 

using namespace std; 

struct node{ 
    string song; 
    node *next; 
}; 

class LinkedList{ 
    private: 
     node *head; 
     int listLength; 
    public: 
     LinkedList(); 
     bool insertNode(node *newnode, int position); 
     bool removenode(int position); 
     void printList(); 
     ~LinkedList(); 
}; 

#endif 

的linkedlist.cpp文件

#include "linkedlist.h" 
#include<iostream> 

LinkedList::LinkedList(){ 
    head = new node; 
    head->song ="head"; 
    head->next=NULL; 
    listLength = 0; 
} 

bool LinkedList::insertNode(node *newnode, int position){ 
    if(position<=0 || position >listLength+1) 
     { 
      cout<<"Error: position is out of range"; 
      return false; 
     } 
    if(head->next == NULL){ 
     head->next = newnode; 
     listLength++; 
     return true; 
    } 
    int count = 0; 
    node *p=head; 
    node *q=head; 
    while(q){ 
     if(position == count){ 
      p->next=newnode; 
      newnode->next = q; 
      listLength++; 
      return true; 
     } 
    p=q; 
    q=p->next; 
    count++; 
    } 
    cout<<"Unable to insert the element due to technical issues"; 
    return false; 
} 

bool LinkedList::removenode(int position){ 
    if(position<=0 || position > listLength+1){ 
     cout<<"Invallid position\n"; 
     return false; 
    } 
    if(head->next ==NULL){ 
     cout<<"The list is already empty\n"; 
     return false; 
    } 
    int count =0; 
    node *q = head; 
    node *p = head; 
    while(q){ 
     if(count==position){ 
     p->next = q->next; 
     delete q; 
     listLength--; 
     return true; 
     } 
    p=q; 
    q=p->next; 
    count++; 
    } 
    cout<<"Error removing elements"; 
    return false; 
} 

void LinkedList::printList(){ 
    int count=0; 
    node *p = head; 
    node *q = head; 

    if(head->next==NULL){ 
     cout<<"The list is empty\n"; 
    } 
    while(count<listLength){ 
     cout<<"\n"<<p->song<<endl; 
     q=p; 
     p=q->next; 
     count++; 
    } 
} 

LinkedList::~LinkedList() 
{ 
    node * p = head; 
    node * q = head; 
    while (q) 
    { 
     p = q; 
     q = p -> next; 
     if (q) delete p; 
    } 
    delete head; 
} 

的main.cpp中是

#include "linkedlist.h" 
#include "linkedlist.cpp" 
#include<iostream> 

using namespace std; 

int main(){ 
    node *A = new node; 
    A->song = "Swatch"; 

    node *B = new node; 
    B->song = "one plus 2"; 

    node *C = new node; 
    C->song = "Woodland"; 

    LinkedList l; 
    l.insertNode(A,1); 
    l.insertNode(B,2); 
    return 0; 
} 

Answer 1

它看起來就像你從來沒有在初始化頭構造函數。這會導致運行時錯誤。您需要添加一條語句，如

head = new node; 

然後記得在您不再需要時刪除它。