C++ 错误 C2819 : type 'List' does not have an overloaded member 'operator ->'

Question

我一直收到这个错误 -

error C2819: type 'List' does not have an overloaded member 'operator ->'

我不明白为什么？帮助？

Main.cpp -

#include <iostream>
#include <string>
#include <cassert>
using namespace std;

#include "List.h"
#include "Node.h"

错误发生在这里:

void PrintList ( List list ) {
 Node * temp = list.getFirst();
 Node * temp2 = list->getLast();
 while ( temp->getItemName() != temp2->getName() ) {
  cout << temp.getItemName() << endl;
 }
}

List.h -

#ifndef LIST_H
#define LIST_H

#include "Node.h"
class List
{
private:
 Node * First;
 Node * Last;
 int num_in_list;
public:
 List () { num_in_list = 0; First = NULL; Last = NULL; }
 int get_num_in_list() { return num_in_list; }
 Node * getFirst() { return First; }
 Node * getLast() { return Last; }
 void del_frnt ();
 void push_front (Node *);
 void push_back (Node *);
 void del_last ();
 void add (Node*);
 Node * pop_back ();
 Node * pop_front ();
 int search_item_list (string);
 Node * get (int);
};
#endif

List.cpp -

#include <iostream>
#include <string>
#include <cassert>
#include "Node.h"
#include "List.h"
using namespace std;

Node * List:: get ( int position_of_node ) {
 assert ( First != NULL);
 Node * temp = First;
 for (int i = 1; i < position_of_node; i++) 
  { temp = temp->getNext(); }
 return temp;
}

int List:: search_item_list (string item_searching_for ) {
 assert (First != NULL && num_in_list != 0);
 int counter = 1;
 Node * temp = First;
 while ( temp->getItemName() != item_searching_for || temp->getNext() == NULL )
  { temp = temp->getNext(); counter++; }
 return counter;
}

void List:: add (Node * node_to_be_added) {
 if (num_in_list == 0) { First = node_to_be_added; Last = node_to_be_added; }
 else if (num_in_list != 0 ) {
  Last->setNext(node_to_be_added);
  node_to_be_added->setPrevous(Last);
  Last = node_to_be_added;
 }
 num_in_list++;
}

Node * List :: pop_back ( ) {
 assert (Last != NULL);
 if ( num_in_list > 1) {
  Node * temp = Last;
  Last = Last->getPrevous();
  Last->setNext(NULL);
  temp->setNext(NULL);
  temp->setPrevous(NULL);
  return temp;
 }
 else if ( num_in_list == 1 ) {
  Node * temp = First;
  First = NULL;
  return temp;
 }
 else return NULL;
}

Node * List:: pop_front ( ) {
 assert ( First != NULL && num_in_list > 0);
 if ( num_in_list > 1 ) {
  Node * temp = First;
  First = First->getNext();
  First->setPrevous(NULL);
  temp->setNext(NULL);
  temp->setPrevous(NULL);
  return temp;
 }

 else if ( num_in_list == 1) {
  Node * temp = First;
  First = NULL;
  return temp;
 }
 else return NULL;
}

void List:: del_last ( ) {
 assert ( Last != NULL );
 if ( num_in_list > 1) {
  Node * temp_node = Last->getPrevous();
  Node * new_last = Last;
  temp_node->setNext(NULL);
  delete new_last;
  num_in_list--;
 }
 else if ( num_in_list == 1) {
  Node * temp = First;
  delete temp;
  num_in_list = 0;
  First = NULL;
 }
}

void List:: del_frnt ( ) {
 assert ( First != NULL);
 if ( num_in_list > 1) {
  Node * saveFirst = First;
  First->getNext()->setPrevous(NULL);
     First = First->getNext( );
     delete saveFirst;
     num_in_list--;
 }
 else if ( num_in_list == 1 ) {
  Node * saveFirst = First;
  delete saveFirst;
  num_in_list = 0;
  First = NULL;
 }
}

void List:: push_back (Node * new_node) {
 assert ( Last != NULL );
 Last->setNext(new_node);
 new_node->setPrevous(Last);
 Last = new_node;
 num_in_list++;
}

void List:: push_front (Node * new_node) {
 if ( First != NULL) {
  First->setPrevous(new_node);
  new_node->setPrevous(NULL);
  new_node->setNext(First);
  First = new_node;
  num_in_list++;
 }
 else if ( First == NULL ) {
  First = new_node;
  Last = new_node;
  num_in_list = 1;
 }
}

Node.h -

#ifndef NODE_H
#define NODE_H
#include <string>
using namespace std;

class Node 
{
private:
 string ItemName;
 string Quantity;
 Node * Next;
 Node * Prevous;
public:
 Node () { ItemName = " "; Quantity = " "; }
 void setItemName (string a) { ItemName = a; }
 string getItemName () { return ItemName; }
 void setQuantity (string a) { Quantity = a; }
 string getQuantity () { return Quantity; }
 void setNext (Node * a) { *Next = *a; }
 Node * getNext () { return Next; }
 void setPrevous (Node * a) { *Prevous = *a; }
 Node * getPrevous () { return Prevous; }
};
#endif

注意:我知道我正在做的只是一个列表，但对于拼贴课我必须这样做:) -任何帮助/指示/如何更好地做事都是太棒了!!!

Answer 1

不能同时做:

Node * temp = list.getFirst();
Node * temp2 = list->getLast();

前者可以工作，因为您按值传递 list，但要使后者工作，您需要重载 operator->。只需使用:

Node * temp2 = list.getLast();

注意:在 C++ 中，访问聚合成员(数据成员或函数)的语法是:

T.member if T is an aggregate type

和

T->member if T is a pointer to an aggregate type

(好的，我已经简化了一点，但这应该可以帮助您入门。)