C++ 列表迭代器,“需要左值作为赋值的左操作数”
我正在为一个课堂作业编制一个循环的双链接列表,我遇到了一些麻烦。当我尝试将迭代器放入我自己的prefix_sum方法或STL版本partial_sum中时,它在*result=val行上给出了一个错误;和*++result=val;部分和的等价行,表示赋值的左操作数需要一个左值。 迭代器的STL版本在我的prefix_sum方法中运行良好,因此我知道迭代器中的某个地方存在问题,但我无法放置它 任何帮助都将不胜感激 我的头文件:C++ 列表迭代器,“需要左值作为赋值的左操作数”,c++,list,templates,iterator,listiterator,C++,List,Templates,Iterator,Listiterator,我正在为一个课堂作业编制一个循环的双链接列表,我遇到了一些麻烦。当我尝试将迭代器放入我自己的prefix_sum方法或STL版本partial_sum中时,它在*result=val行上给出了一个错误;和*++result=val;部分和的等价行,表示赋值的左操作数需要一个左值。 迭代器的STL版本在我的prefix_sum方法中运行良好,因此我知道迭代器中的某个地方存在问题,但我无法放置它 任何帮助都将不胜感激 我的头文件: #ifndef LIST_H #define LIST_H #in
#ifndef LIST_H
#define LIST_H
#include <string>
#include <iostream>
template<class T>
struct Node
{
Node* prev;
Node* next;
T val;
Node():prev(this), next(this) {}
Node(T aValue) :prev (this), next(this), val(aValue) {}
};
template<class T>
class s_list
{
public:
struct iterator
{
typedef std::bidirectional_iterator_tag iterator_category;
typedef std::ptrdiff_t difference_type;
typedef T value_type;
typedef T * pointer;
typedef T &reference;
public:
// Constructors:
iterator() :cur(new Node<T>()) {}
// Operatoral Overloads
T operator *() {return cur->val;}
bool operator == (const iterator an_iter) {return (cur == an_iter.cur);}
bool operator != (const iterator an_iter) {return (cur != an_iter.cur);}
iterator& operator ++ () {cur = cur->next; return *this;}
iterator& operator -- () {cur = cur->prev; return *this;}
iterator operator ++ (int)
{
iterator temp = *this;
cur = cur->next;
return temp;
}
iterator operator -- (int)
{
iterator temp = *this;
cur = cur->prev;
return temp;
}
friend class s_list;
private:
iterator(Node<T>* to_iter):cur(to_iter) {}
Node<T>* cur;
};
// Constructors:
s_list() : head(new Node<T>()){}
s_list(const s_list<T>& aList) : head(new Node<T>()) {...}
// Destructor:
virtual ~s_list() {clear(); delete head;}
// Iterator Methods:
iterator begin() {return (iterator(head->next));}
iterator end() {return (iterator(head));}
void push_back(T aVal) {...}
void push_front(T aVal) {...}
void insert(iterator pos, T aVal) {...}
int size() {...}
bool empty() {return (head->next == head->prev);}
inline void erase(iterator to_del);
inline void erase(iterator from, iterator to);
void clear(){erase(head->next, head);}
//inline void prefix_sum(iterator start_sum, iterator end_sum, iterator write_to);
// Operational Overloads:
inline void operator = (const s_list<T>& aList);
private:
Node<T>* head;
};
template <class iterator_in, class iterator_out>
iterator_out prefix_sum (iterator_in first, iterator_in last, iterator_out result)
{
std::cerr << "\n*result = " << *result << '\n';
if (first != last) {
typename std::iterator_traits<iterator_in>::value_type val = *first;
*result = val;
while (++first != last) {
val = val + *first;
*++result = val;
}
++result;
}
return result;
}
#endif // LIST_H
我的简化实施文件:
/**
* @date 24 November, 2013
* @brief Linked List 6
* @file HW7.cpp
*
* @note
* This work is licensed under a Creative Commons Attribution-NonCommercial 3.0
* Unported License.
*
* Permission is granted to copy, distribute, transmit, and/or adapt this software
* for any and all noncommercial purposes.
*
* For details, see:
* https://creativecommons.org/licenses/by-nc/3.0/
*/
#include "s_list.h"
#include <iostream>
#include <sstream>
#include <list>
#include <numeric>
for(int i = 1; i < 10; i++)
{
stlList.push_back(i);
myList.push_back(i);
}
std::cout << "\nOriginal myList:\n";
typename s_list<int>::iterator myIter = myList.begin();
while (myIter != myList.end()){
std::cout << *myIter << " ";
++myIter;
}
std::cout << "\nOriginal stlList:\n";
std::_List_iterator<int> stlIter = stlList.begin();
while (stlIter != stlList.end()){
std::cout << *stlIter << " ";
++stlIter;
}
std::partial_sum(myList.begin(), myList.end(), (myList.begin()));
prefix_sum(myList.begin(), myList.end(), myList.begin());
prefix_sum(stlList.begin(), stlList.end(), stlList.begin());
std::cout << "\nResult after running myList with STL partial_sum() algorithm\n";
myIter = myList.begin();
while(myIter != myList.end()){
std::cout << *myIter << " ";
++myIter;
}
std::cout << "\nResult after running STL list with my prefix_sum() algorithm\n";
stlIter = stlList.begin();
while (stlIter != stlList.end()){
std::cout << *stlIter<< " ";
++stlIter;
}
}
这不起作用的原因是您没有正确地重载运算符:运算符*应该返回对T的引用,如下所示:
T& operator *() { return cur->val; }
^
|
+-- Return type needs to be a reference type.
请注意,由于您正在定义自己的迭代器,因此还应该为中缀运算符->提供重载。您还应该提供一对常量重载,因此最终应该有以下四个运算符:
T& operator*();
const T& operator*() const;
T* operator->();
const T* operator->() const;
也很东西。只包括对我们解决问题有用的代码,而不是所有的东西,包括关于它的评论。我精简了它,但在我完成时已经得到了一个答案。加当斯,这非常有效。我绞尽脑汁想解决这个问题好几天了,就是这么简单。我奖励你一个免费的互联网,因为你遇到了麻烦。价值观从来都不是参考。你是说退货类型吗?