From aa0156b24bd81ca20ddda5a4357587e76a580d7d Mon Sep 17 00:00:00 2001 From: codkk Date: Thu, 19 May 2022 14:43:42 +0800 Subject: [PATCH 1/2] =?UTF-8?q?=E4=B8=A4=E4=B8=AA=E9=97=AE=E9=A2=98?= =?UTF-8?q?=E6=B2=A1=E5=81=9A=E5=87=BA=E6=9D=A5=EF=BC=8C=E5=85=B6=E5=AE=83?= =?UTF-8?q?=E5=AE=8C=E6=88=90=E4=BA=86?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- main.cpp | 52 +++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 39 insertions(+), 13 deletions(-) diff --git a/main.cpp b/main.cpp index dc25c6b..cf1e42e 100644 --- a/main.cpp +++ b/main.cpp @@ -1,7 +1,6 @@ /* 基于智能指针实现双向链表 */ #include #include - struct Node { // 这两个指针会造成什么问题？请修复 std::shared_ptr next; @@ -10,9 +9,8 @@ struct Node { int value; - // 这个构造函数有什么可以改进的？ - Node(int val) { - value = val; + // 这个构造函数有什么可以改进的？//使用初始化列表，不用等创建后再初始化赋值即可以在创建时赋值。 + Node(int val):value(val) { } void insert(int val) { @@ -33,7 +31,7 @@ struct Node { } ~Node() { - printf("~Node()\n"); // 应输出多少次？为什么少了？ + printf("~Node(%d)\n",this->value); // 应输出多少次？为什么少了？//prev清除了但next没有清除，智能指针引用没有清零，需要手动erase或者使用弱指针或uniptr } }; @@ -44,14 +42,42 @@ struct List { List(List const &other) { printf("List 被拷贝！\n"); - head = other.head; // 这是浅拷贝！ + printf("拷贝构造函数\n"); + //head = other.head; // 这是浅拷贝！ // 请实现拷贝构造函数为 **深拷贝** + std::shared_ptr currnode;//用于记录尾结点 + for(auto curr = other.front(); curr; curr = curr->next.get()) + { + auto node = std::make_shared(curr->value); + if(head) + { + node->prev = currnode; + currnode->next = node; + } + else + { + head = node; + } + currnode = node; + } } - List &operator=(List const &) = delete; // 为什么删除拷贝赋值函数也不出错？ + List &operator=(List const &other) = delete; // 为什么删除拷贝赋值函数也不出错？// 转而默认调用移动赋值函数。先创建一个即时对象，移动到目标对象上。 List(List &&) = default; - List &operator=(List &&) = default; + List &operator=(List &&other)//移动赋值 + { + printf("移动赋值函数\n"); + printf("先解构原来的\n");; + for(auto curr = this->front(); curr; curr=curr->next.get()) + { + curr->erase(); + } + printf("再移动Head\n"); + this->head = other.head; + other.head = nullptr; + return *this; + } Node *front() const { return head.get(); @@ -80,7 +106,7 @@ struct List { } }; -void print(List lst) { // 有什么值得改进的？ +void print(const List& lst) { // 有什么值得改进的？//使用常引用，减少拷贝构造 printf("["); for (auto curr = lst.front(); curr; curr = curr->next.get()) { printf(" %d", curr->value); @@ -89,7 +115,7 @@ void print(List lst) { // 有什么值得改进的？ } int main() { - List a; + List a; //无参构造a a.push_front(7); a.push_front(5); @@ -105,15 +131,15 @@ int main() { print(a); // [ 1 4 2 8 5 7 ] - List b = a; + List b = a; //拷贝a构造b， 深拷贝 a.at(3)->erase(); print(a); // [ 1 4 2 5 7 ] print(b); // [ 1 4 2 8 5 7 ] - b = {}; - a = {}; + b = {};//默认构造一个{}， 移动赋值到b， b原来的元素应该被释放 + a = {};//默认构造一个{}， 移动赋值到a， a原来的元素应该被释放 return 0; } From 4161f9b8d11f2534cd5d1ca6f8f09d5791d08888 Mon Sep 17 00:00:00 2001 From: codkk Date: Sun, 22 May 2022 22:25:35 +0800 Subject: [PATCH 2/2] =?UTF-8?q?next=E5=92=8Cprev=E6=94=B9=E4=B8=BAunique?= =?UTF-8?q?=5Fptr=E5=92=8C=E5=8E=9F=E5=A7=8B=E6=8C=87=E9=92=88?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- main.cpp | 58 ++++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 37 insertions(+), 21 deletions(-) diff --git a/main.cpp b/main.cpp index cf1e42e..b66fdbd 100644 --- a/main.cpp +++ b/main.cpp @@ -3,8 +3,10 @@ #include struct Node { // 这两个指针会造成什么问题？请修复 - std::shared_ptr next; - std::shared_ptr prev; + //std::shared_ptr next; + //std::shared_ptr prev; + std::unique_ptr next; + Node* prev; // 如果能改成 unique_ptr 就更好了! int value; @@ -14,20 +16,22 @@ struct Node { } void insert(int val) { - auto node = std::make_shared(val); - node->next = next; + auto node = std::make_unique(val); + node->next = std::move(next); node->prev = prev; if (prev) - prev->next = node; + prev->next = std::move(node); if (next) - next->prev = node; + next->prev = node.get(); } void erase() { - if (prev) - prev->next = next; if (next) next->prev = prev; + if (prev){ + //prev->next = nullptr;//不能置为nullptr，否则链表当前节点之后的会全部解构。 + prev->next = std::move(next); + } } ~Node() { @@ -36,7 +40,9 @@ struct Node { }; struct List { - std::shared_ptr head; + //std::shared_ptr head; + //Node* head{nullptr}; + std::unique_ptr head; List() = default; @@ -45,20 +51,22 @@ struct List { printf("拷贝构造函数\n"); //head = other.head; // 这是浅拷贝！ // 请实现拷贝构造函数为 **深拷贝** - std::shared_ptr currnode;//用于记录尾结点 + Node* tailnode;//用于记录尾结点 for(auto curr = other.front(); curr; curr = curr->next.get()) { - auto node = std::make_shared(curr->value); + auto node = std::make_unique(curr->value); if(head) { - node->prev = currnode; - currnode->next = node; + node->prev = tailnode; + tailnode->next = std::move(node); + tailnode = tailnode->next.get(); } else { - head = node; + head = std::move(node); + tailnode = head.get(); } - currnode = node; + } } @@ -74,7 +82,7 @@ struct List { curr->erase(); } printf("再移动Head\n"); - this->head = other.head; + this->head = std::move(other.head); other.head = nullptr; return *this; } @@ -85,16 +93,24 @@ struct List { int pop_front() { int ret = head->value; - head = head->next; + head = std::move(head->next); return ret; } void push_front(int value) { - auto node = std::make_shared(value); - node->next = head; + auto node = std::make_unique(value); if (head) - head->prev = node; - head = node; + { + head->prev = node.get(); + Node* tmp = head.get(); + node->next = std::move(head); + head = std::move(node); + } + else + { + //node->next = std::move(head); + head = std::move(node); + } } Node *at(size_t index) const {