C++；链表包含（）函数 我对C++是很新的，并且在插入链接（）函数中使用链接表有困难。以下是我收到的代码，从以下开始： #include <iostream> #include <cassert> #include <stdexcept> using namespace std; template<typename T> class mylist; template<typename T> ostream& operator<< (ostream &out, const mylist<T> &l); template <typename T> class mylist { public: // node definition struct node { T data; node* next_ptr; // node constructor node(const T &d, node* n):data(d),next_ptr(n){} }; // alternative node definition /* class node { public: T data; node* next_ptr; // node constructor node(const T&d, node* n):data(d),next_ptr(n){} }; */ // linked list head pointer node* head_ptr; //friend ostream& operator<< <>(ostream& out, const mylist<T>&l); friend ostream& operator<< (ostream &out, const mylist<T> &l); public: // default constructor mylist():head_ptr(nullptr) {} // head_ptr points nowhere // adds element to the front of the linked list void push_front(const T &elem) { head_ptr = new node(elem, head_ptr); } // check if linked list is empty bool empty() { return head_ptr == nullptr;} // number of nodes in linked list unsigned size() { return length();} unsigned length() { unsigned l = 0; for(node* current = head_ptr; current != nullptr; current = current->next_ptr) { ++l; } return l; } // copy constructor mylist(const mylist &other) { for(node* current_other = other.head_ptr; current_other != nullptr; current_other = current_other->next_ptr) { this.push_back(current_other->data); // inefficient, but easy :) } } // destructor ~mylist() { node* tmp; for(node* current = head_ptr; current != nullptr; current = tmp) { tmp=current->next_ptr; delete current; } } // at accessor method (returns the element at the ith position in the linked list) T& at(unsigned i){ unsigned l=0; node* current; for(current = head_ptr; current != nullptr; current = current->next_ptr) { if(l == i) break; ++l; } if (current == nullptr) throw out_of_range("index i is out of range"); else return current->data; } // bracket operator (returns the element at the ith position in the linked list) T& operator[](unsigned i){ return at(i); } // adds element to the end of the linked list void push_back(const T &elem) { if(empty()) { push_front(elem); return; } node* last_ptr; for(last_ptr = head_ptr; last_ptr->next_ptr != nullptr; last_ptr = last_ptr->next_ptr); last_ptr->next_ptr = new node(elem, nullptr); } // prints the contents of the linked list void print_all(void) { cout << "mylist{"; for(node* current_ptr = head_ptr; current_ptr != nullptr; current_ptr = current_ptr->next_ptr){ cout << current_ptr->data << " "; } cout << "}" << endl; }

我的问题是我遇到了以下错误，我不知道如何修复它，也不知道它意味着什么：

1>c:\users\jaysen\documents\data structures\lab 2\lab 2\mylist_tpt.h(184): error C2512: 'mylist<T>::node' : no appropriate default constructor available
1>          with
1>          [
1>              T=std::string
1>          ]
1>          c:\users\jaysen\documents\data structures\lab 2\lab 2\mylist_tpt.h(182) : while compiling class template member function 'void mylist<T>::insert(const T &,unsigned int)'
1>          with
1>          [
1>              T=std::string
1>          ]
1>          c:\users\jaysen\documents\data structures\lab 2\lab 2\mylist_main.cpp(20) : see reference to class template instantiation 'mylist<T>' being compiled
1>          with
1>          [
1>              T=std::string
1>          ]

1>c:\users\jaysen\documents\data structures\lab 2\lab 2\mylist\u tpt.h（184）：错误C2512:“mylist:：node”：没有合适的默认构造函数可用
1> 与
1>          [
1> T=std:：string
1>          ]
1> c:\users\jaysen\documents\data structures\lab 2\lab 2\mylist\u tpt.h（182）：编译类模板成员函数“void mylist:：insert（const T&，unsigned int）”时
1> 与
1>          [
1> T=std:：string
1>          ]
1> c:\users\jaysen\documents\data structures\lab 2\lab 2\mylist\u main.cpp（20）：请参阅正在编译的类模板实例化“mylist”的参考
1> 与
1>          [
1> T=std:：string
1>          ]

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提前谢谢你能给我的任何帮助

尝试将

const

cualifier添加到

empty

函数中：

bool empty() const { return head_ptr == nullptr;}

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此错误与问题标题无关。请重新阅读错误，尤其是文件名和行号。您的想法非常有效！我现在的插入函数有问题。。。我已将问题中的代码更改为新代码。如@JoachimPileborg所述，错误消息包含修复错误所需的所有信息。是的，我必须承认这个错误信息很难阅读，但是再多练习一下，你就会习惯阅读它了。关于你的新问题，我想（因为你还没有发布行号）在某个地方需要一个节点类的默认构造函数（可能是在复制自定义列表时），但是，由于问题主题的改变，我认为最好打开一个新问题。

bool empty() const { return head_ptr == nullptr;}