问题描述
我正在尝试按照 Stroustrup 的书“使用 C++ 的原则和实践”，第 20.4 章实现模板化双链表。我想使用唯一指针，而不是原始指针。 代码组织如下：
特别是，我目前对 iterator insert(iterator p,const T& x) 方法的实现感兴趣，该方法将 x 插入列表中的 p 之后。它可以编译，但是当我运行它时，我可以看到插入正确执行，然后出现分段错误，我坚信这是因为我在使用唯一指针时犯了一些错误。下面是insert方法的实现
iterator insert(iterator position,const T& value) {
auto newNode = new Node::Node<T>(value,position.current->next.get(),position.current);
if (position.current == last ) {
last.reset(newNode);
}
position.current->next.release();
position.current->next.reset(newNode);
++_size;
return position;
}
这是我的 Node.h
#ifndef Node_h
#define Node_h
#include <algorithm>
#include <iostream>
#include <memory> // std::unique_ptr
#include <utility> // std::move
namespace Node {
template <typename T>
struct Node {
T data;
std::unique_ptr<Node> next;
Node* prevIoUs;
Node() noexcept = default;
explicit Node(const T& _data) : data{_data},next{nullptr},prevIoUs{nullptr} {
std::cout << "l-value"<<std::endl;
}
Node(const T& _data,Node* _next,Node* _prevIoUs): data{_data},next{_next},prevIoUs{_prevIoUs} {}
explicit Node(T&& x) : data{std::move(x)} {
std::cout << "r-value" << std::endl;
}
Node(T&& x,Node* _prevIoUs) : data{std::move(x)},prevIoUs{_prevIoUs} {
std::cout << "r-value" << std::endl;
}
explicit Node(const std::unique_ptr<Node> &x) : data{x->data} {
if (x->next){
next.reset(new Node{x->next});
}
// if (x->prevIoUs){
// prevIoUs.reset(new Node{x->prevIoUs});
// }
}
~Node()=default;
//Move semantics,copy semantics
void printNode(){
std::cout << "Data is: " << data <<"\n";
}
};
} //end namespace
#endif /* Node_h */
然后，这是 Iterator.h
#ifndef Iterator_h
#define Iterator_h
#include "Node.h"
#include <iterator>
template <typename T >
struct __iterator {;
using NodeT = Node::Node<T>;
NodeT* current;
//public:
using value_type = T;
using difference_type = std::ptrdiff_t;
using iterator_category = std::forward_iterator_tag;
using reference = value_type&;
using pointer = value_type *;
explicit __iterator(NodeT* p) : current{p} {}
__iterator() noexcept=default;
~__iterator()=default;
reference operator*() const noexcept{
return current->data;
}
pointer operator->() const noexcept{
return &**this;
}
__iterator& operator++() {
current = current->next.get();
return *this;
}
__iterator& operator--(){
current=current->prevIoUs; //prevIoUs is just a raw pointer
return *this;
}
friend bool operator==(__iterator &a,__iterator &b) {
return a.current == b.current;
}
friend bool operator!=(__iterator &a,__iterator &b) { return !(a == b); }
};
#endif /* Iterator_h */
这是标题 List.h
#include "Iterator.h"
#include <cassert>
template <typename T>
class List {
private:
std::unique_ptr<Node::Node<T>> first;
std::unique_ptr<Node::Node<T>> last;
int _size;
public:
using iterator = __iterator<T>;
iterator begin(){return iterator{first.get()};}
iterator end(){return iterator{nullptr};} //one past the last
iterator go_to(const int n){
assert(n>=0);
int i=0;
if (n < _size) {
auto tmp{begin()};
while (i<n) {
++tmp;
++i;
}
return tmp;
}else{
return iterator{nullptr};
}
}
List() : first{nullptr},last{nullptr},_size{0} {}
~List() noexcept = default;
template <typename O>
void push_front(O &&x) { // forwarding ref. not r-value
first.reset(new Node::Node<T>{std::forward<O>(x),first.release(),nullptr});
if (_size==0) {
last.reset(nullptr);
}
++_size;
}
template <typename O> //forward reference
void push_back(O&& x){
auto tmp = first.get();
auto _node = new Node::Node<T>{std::forward<O>(x)};
if (!tmp) {
first.reset(_node);
return;
}
while (tmp->next) {
tmp = tmp->next.get();
}
tmp->next.reset(_node);
++_size;
}
iterator substitute(iterator p,const T& x){
//_size must not be incremented!
iterator tmp{p};
if(tmp.current){
*tmp = x;
return tmp;
}else{
return iterator{nullptr};
}
}
iterator insert(iterator position,position.current);
std::cout << position.current << std::endl;
if (position.current == last.get() ) {
last.reset(newNode);
}
position.current->next.release(); //otherwise: "pointer being freed was not allocated"
position.current->next.reset(newNode); //set next of prevIoUs node to newNode
++_size;
return position;
}
friend std::ostream& operator<<(std::ostream& os,List& l){
auto itStop = l.end();
os << "The list has " << l._size << " elements"<<"\n";
for (auto it = l.begin(); it!=itStop; ++it) {
os<< *it << " ";
}
return os;
}
};
最后，这是包含测试的 main.cpp 文件：
#include "List.h"
int main() {
List<int> l{};
int i=8;
l.push_front(i); //l-value
l.push_back(4); //r-value
l.push_back(i+2); //r-value
l.push_back(95); //r-value
l.push_front(29); //l-value
l.push_front(i*i); //r-value
std::cout << "My list so far: " << l<<std::endl;
auto p{l.go_to(3)};
auto itt = l.substitute(p,29);
std::cout << "My list after substitution: \t" << l<<std::endl;
auto pp{l.go_to(2)};
auto it2 = l.insert(pp,98);
std::cout << "My list after insertion: \t" << l<<std::endl;
auto it3= l.insert(--pp,998);
std::cout << "My list after insertion: \t" << l<<std::endl;
return 0;
}
解决方法
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