c++Primer第十二章：动态内存

客官°小女子只卖身不卖艺 2023-01-16 15:23 128阅读 0赞

### 目录 ###

*  智能指针
 *   *  shared\_ptr
     *   *  一般操作
         *  内存释放过程
         *  代码测试
     *  shared\_ptr与new与list
     *   *  常见定义和修改shared\_ptr的其他方法
     *  unique\_ptr
     *   *  常用操作
     *  weak\_ptr
 *  代码测试
 *  new delet
 *  allocator
 *  文本查询代码

# 智能指针 #

## shared\_ptr ##

允许多个指针指向同一对象  
自动完成销毁工作，自动释放关联内存

### 一般操作 ###

与new无关的初始化

shared_ptr<T> p(q);
    shared_ptr<string> p = make_shared<string>(10,'9');
    auto p = make_shared<T>(q);//q可以为空 ()

检查是否为空

if(p&&p->empty())

shared\_ptr 与unique\_ptr都支持的操作

<table> 
 <thead> 
  <tr> 
   <th>项目</th> 
   <th>Value</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>shared_ptr&lt; T &gt; sp</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>unique_ptr&lt; T &gt; up</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>p</td> 
   <td>作为判断条件</td> 
  </tr> 
  <tr> 
   <td>*p</td> 
   <td>获取其对象</td> 
  </tr> 
  <tr> 
   <td>p.get()</td> 
   <td>返回p中保存的指针</td> 
  </tr> 
  <tr> 
   <td>p.swap(q)</td> 
   <td></td> 
  </tr> 
  <tr> 
   <td>swap(p,q)</td> 
   <td></td> 
  </tr> 
 </tbody> 
</table>

shared\_ptr独有的操作

<table> 
 <thead> 
  <tr> 
   <th>项目</th> 
   <th>Value</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>p=q</td> 
   <td>p指向q,q的引用计数+1</td> 
  </tr> 
  <tr> 
   <td>p.unique()</td> 
   <td>p.use_count()=1t rue</td> 
  </tr> 
  <tr> 
   <td>p.use_count()</td> 
   <td></td> 
  </tr> 
 </tbody> 
</table>

### 内存释放过程 ###

shared_ptr<f> factory(T arg){
    	return make_shared<f>(arg);
    }
    void use_factory(T arg){
    	auto p = factory(arg);
    	//p使用过程，一旦离开了作用域指向的内存会自动释放
    }
    
    //但是use_factory如果是这种就不会
    shared_ptr<f> use_factory(T arg){
    	auto p = factory(arg);
    	return p;
    }

### 代码测试 ###

shared_ptr<int> w(new int(100));
    	cout<<w.use_count()<<endl;
    	auto w1 = w;
    	int * p = w.get();
    	cout<<"w.use_count()="<<w.use_count()<<endl;
    	cout<<"w1.use_count()="<<w1.use_count()<<endl;
    	w1 = nullptr;
    	cout<<"w.use_count()="<<w.use_count()<<endl;
    	cout<<"w1.use_count()="<<w1.use_count()<<endl;
    	cout<<"p="<<*p<<endl;
    	w = nullptr;
    	cout<<"p="<<*p<<endl;
    	w.reset(new int (1024));
    	cout<<"w="<<*(w.get())<<endl;

结果  
![在这里插入图片描述][20210426133415866.png]

## shared\_ptr与new与list ##

### 常见定义和修改shared\_ptr的其他方法 ###

不要用get进行赋值

auto temp = shared_ptr<int>(new int(p))
    //管理q所指对象，q必须指向new分配的内存，且能转换为T*类型
    shared_ptr<T> p(q);
    //接管unique_ptr 并将其置空
    shared_ptr<T> p(u);
    //接管q，q能转换为T*类型，p使用d来代替delete
    shared_ptr<T> p(q,d);
    //p是p2拷贝，唯一的区别是后面
    shared_ptr<T> p(p2,d);
    //若p是唯一指向该对象的智能指针，则会释放此对象
    p.reset();
    //若p是唯一指向该对象的智能指针，则会释放此对象，p指向q
    p.reset(q);
    //同时调用d来释放q
    p.reset(q,d);

例如，删除时自动调用del  
如果智能指针管理的资源不是new分配的内存，记得传递一个删除器，尤其是管理链接资源的时候

bool del(int *p){ 
        delete [] p;
    }
    
    shared_ptr<int> shared(new int[100],del);//使用函数
    
    shared_ptr<int> ptr(new int[100],
    [](int *p){ delete [] p;});//使用lambda表达式

保留list，删空间

list<int*> l1;
    	int n=10;
    	while(n--){ 
    		int *p = new int(n);
    		l1.push_back(p);
    	}
    	cout<<"list:"<<endl;
    	for(auto e: l1){ 
    		cout<<*e<<" ";
    	}
    	cout<<endl;
    	int *temp = (int*)*(l1.begin());
    	cout<<"temp="<<*temp<<endl;
    	for(auto e= l1.begin();e!=l1.end();){ 
    		int *p=(int*)*e;
    		//e = l1.erase(e);
    		cout<<*(*e)<<endl;
    		e++;
    		delete p;
    	}
    	for(auto e: l1){ 
    		cout<<*e<<" ";
    	}
    	cout<<l1.size()<<endl;
    	cout<<"temp="<<*temp<<endl;
    	cout<<endl;

结果：内存中的值都已经释放了  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY3MjQwNA_size_16_color_FFFFFF_t_70]  
list与空间全删

list<int*> l1;
    	int n=10;
    	while(n--){ 
    		int *p = new int(n);
    		l1.push_back(p);
    	}
    	cout<<"list:"<<endl;
    	for(auto e: l1){ 
    		cout<<*e<<" ";
    	}
    	cout<<endl;
    	int *temp = (int*)*(l1.begin());
    	cout<<"temp="<<*temp<<endl;
    	for(auto e= l1.begin();e!=l1.end();){ 
    		int *p=(int*)*e;
    		//if()
    			delete p;
    			e = l1.erase(e);
    		//else e++;
    	}
    	cout<<"again:"<<endl;
    	for(auto e: l1){ 
    		cout<<*e<<" ";
    	}
    	cout<<endl;
    	cout<<"size="<<l1.size()<<endl;
    	cout<<"temp="<<*temp<<endl;
    	cout<<endl;
    	return 0;

结果  
![在这里插入图片描述][2021042614281889.png]  
list 智能指针释放空间

list<shared_ptr<int>> sp;
    	int n=10;
    	while(n--){ 
    		shared_ptr<int> temp(new int (n));
    		sp.push_back(temp);
    	}
    	for(auto e:sp){ 
    		cout<<*e<<" ";
    	}
    	cout<<endl;
    	auto temp = sp.begin();
    	cout<<*(*temp)<<endl;
    	sp.erase(sp.begin());
    	cout<<*(*temp)<<endl;

结果，erase之后 自动释放空间了，比直接delet方便  
![在这里插入图片描述][2021042615160023.png]

## unique\_ptr ##

### 常用操作 ###

unique_ptr<T> u1
    unique_ptr<T> u2
    unique_ptr<T,D> u(d)
    u = nullptr
    //放弃控制权
    u.release()
    //释放对象
    u.reset()
    u.reset(q)
    u.reset(nulptr)

## weak\_ptr ##

不增加计数值

weak_ptr<T> w
    weak_ptr<T> w(sp)
    //p可以是weak_ptr,shared_ptr
    w=p
    w.reset()
    w.use_count()
    //use_count = 0 ture
    w.expired()
    //expired = 0 返回空shared_ptr否则返回一个指向w的对象shared_ptr
    w.lock()

# 代码测试 #

StrBlobPtr.h

#ifndef STRBLOBPTR
    #define STRBLOBPTR
    #include<iostream>
    #include<memory>
    #include<vector>
    #include<string>
    #include"StrBlob.h"
    using namespace std;
    class StrBlob;
    class StrBlobPtr
    { 
    private:
        //若检查成功返回一个指向vector的shared_ptr
        shared_ptr<vector<string>> check(size_t,const string &)const;
        //指向一个vector<string>的weak_ptr
        weak_ptr<vector<string>> wptr;
        //在数组中的当前位置
        size_t curr;
    public:
        StrBlobPtr():curr(0){ };
        StrBlobPtr(StrBlob &b,size_t sz=0):wptr(b.data),curr(sz){ };
        int wptr_use_count(){ return wptr.use_count();};
        string &deref() const;
        //前缀递增
        StrBlobPtr& incr();
    };
    #endif

StrBlobPtr.cpp

#include"StrBlobPtr.h"
    //弱指针可以返回共享指针
    shared_ptr<vector<string>> StrBlobPtr::check(size_t i,const string &msg)const{ 
        //vector是否还存在
        auto ret = wptr.lock();
        if(!ret)
            throw runtime_error("unbound StrBlobPtr");
        if(i>ret->size())
            throw out_of_range(msg);
        return ret;
    }
    
    string &StrBlobPtr::deref() const{ 
        auto p = check(curr,"dereference past end");
        //对象所指的Vector
        return (*p)[curr];
    }
    
    StrBlobPtr &StrBlobPtr::incr(){ 
        check(curr,"increment past end of StrBlobPtr");
        ++curr;
        return *this;
    }

StrBlob.cpp

#include"StrBlob.h"
    #include"StrBlobPtr.h"
    void StrBlob::check (size_type i ,const string &t)const{ 
        if(i>=data->size())
            throw out_of_range(t);
    }
    string& StrBlob::front(){ 
        check(0,"front on empty StrBlob");
        return data->front();
    }
    
    string & StrBlob::back(){ 
        check(0,"back on empty StrBlob");
        return data->back();
    }
    void StrBlob::pop_back(){ 
        check(0,"pop_back on empty StrBlob");
        data->pop_back();
    }
    //StrBlobPtr(StrBlob &b,size_t sz=0)
    StrBlobPtr StrBlob::begin(){ 
        return StrBlobPtr(*this);
    }
    //StrBlobPtr(StrBlob &b,size_t sz=0){..cur(sz)}
    StrBlobPtr StrBlob::end(){ 
            auto ret = StrBlobPtr(*this,data->size()-1);return ret;
    }

StrBlob.h

//shared_ptr 使用
    #ifndef STRBLOB
    #define STRBLOB
    #include<iostream>
    #include<string>
    #include<memory>
    #include<vector>
    using namespace std;
    typedef vector<string>::size_type size_type;
    class StrBlobPtr;
    class StrBlob
    { 
    private:
        //共享的数据
        shared_ptr<vector<string>> data;
        //抛出异常
        void check(size_type i,const string &t) const;
    public:
        friend class StrBlobPtr;
        //默认构造分配一个空vector
        StrBlob():data(make_shared<vector<string>>()){ }
        //make_shared :返回一个shared_ptr 以il初始化vector<string>对象
        StrBlob(initializer_list<string> il):data(make_shared<vector<string>>(il)){ };
        int data_use_count(){ return data.use_count();}
        
        
        
        //返回对象的长度
        
        
        size_type size()const { return data->size();};
        bool empty()const { return data->empty();};
    
    
    
        //添加删除
        void push_back(const string &t){ data->push_back(t);};
        void pop_back();
        //元素访问
        string & front();
        string & back();
    
        //出现error: invalid use of incomplete type 'class StrBlob'
        StrBlobPtr begin(); //{return StrBlobPtr(*this);}
        StrBlobPtr end(); //{auto ret = StrBlobPtr(*this,data->size());return ret;}
    };
    #endif

main.cpp

StrBlob b2;
        StrBlob b1 = { "a","an","the"};
        cout<<"use_count="<<b1.data_use_count()<<endl;
        b2 = b1;
        cout<<"use_count="<<b1.data_use_count()<<endl;
        b2.push_back("about");
        cout<<"b1.size = "<<b1.size()<<endl;
        cout<<"b2.size = "<<b2.size()<<endl;
        cout<<"b1.front = "<<b1.front()<<endl;
        cout<<"b2.front = "<<b2.front()<<endl;
        cout<<"b1.begin().def()="<<b1.begin().deref()<<endl;
        cout<<"b2.begin().def()="<<b2.begin().incr().deref()<<endl;
        cout<<"b1.end().def()="<<b1.end().deref()<<endl;
        StrBlobPtr b3(b1);
        b3.incr();
        b3.incr();
        //b3内部是弱指针 所以不会添加use_count;
        cout<<"b3.deref()="<<b3.deref()<<endl;
        cout<<"b2.begin().def()="<<b2.begin().incr().deref()<<endl;
        cout<<"b3.deref()="<<b3.deref()<<endl;
        cout<<"use_count="<<b1.data_use_count()<<endl;
        cout<<"use_count="<<b3.wptr_use_count()<<endl;

结果  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY3MjQwNA_size_16_color_FFFFFF_t_70 1]

# new delet #

delete p;
    delete [] pa;

unique\_ptr 自动调用删除器进行数组管理

unique_ptr<int[]> up(new int[10]);
    up.release();

shared\_ptr必须自己提供删除器

shared_ptr<int> sp(new int[10],[](int *p){delete[] p;});
    sp.reset();

# allocator #

p427写不动了······感觉用的也少

# 文本查询代码 #

TextQuery.cpp

#include"TextQuery.h"
    
    //make_plural(wc, "word ", "s ")当输入中文本中,word数大于一是在word后加s，为words为word的复数！
    string make_plural(size_t ctr,const string &word, const string &ending)
    { 
      return (ctr==1) ? word : word+ending;                                           
    }
    ostream &print(ostream &os,const QueryResult &qr){ 
        os<<qr.sought<<" occurs "<<qr.lines->size()<<" "<<make_plural(qr.lines->size(),"times","s")<<endl;
        for(auto num: *qr.lines){ 
            os<<"\t(line "<<num+1<<")"<<*(qr.file->begin() + num)<<endl;
        }
        return os;
        
    }
    
    
    //share指针只能直接初始化，所以再函数后面接着
    TextQuery::TextQuery(ifstream & is):file(new vector<string>)
    { 
        string text;
        //逐行读取
        while(getline(is,text)){ 
            //保存每一行
            file->push_back(text);
            //行号
            int n = file->size()-1;
            istringstream line(text);
            string word;
            //分解每一行的单词
            while(line>>word){ 
                //不在就加入，在则插行号 或者可以使用引用
                //auto &line = wm[word];
                if(!wm[word])
                    //分配一个新set
                    wm[word].reset(new set<line_no>);
                wm[word]->insert(n);
                
            }
    
        }
    }
    
    TextQuery::~TextQuery()
    { 
        cout<<"TextQuery End"<<endl;
    }
    
    QueryResult TextQuery::query(const string &sought) const{ 
        //如果没有找到就返回一个指向此set的指针 没懂为什么是静态的
        static shared_ptr<set<line_no>> nodata(new set<line_no>);
        //查找到的单词所对应的set
        auto loc = wm.find(sought);
        if(loc == wm.end())
            return QueryResult(sought,nodata,file);
        else
            return QueryResult(sought,loc->second,file); 
    }
    
    void runQueries(ifstream &infile){ 
        TextQuery tq(infile);
        while ((true))
        { 
            cout<<"endter word to look for,or q toquit: "<<endl;
            string s;
            //cout<<"cin s"<<endl;
            cin>>s;
            //cout<<"cout s"<<endl;
            if(s == "q"){ 
                break;
            }
            //cout<<"print s"<<endl;
            print(cout,tq.query(s))<<endl;
        }
        
    }

TextQuery.h

#ifndef TEXTQUERY
    #define TEXTQUERY
    #include<iostream>
    #include<string>
    #include<vector>
    #include<memory>
    #include<fstream>
    #include<map>
    #include<set>
    #include<sstream>
    using namespace std;
    typedef vector<string>::size_type line_no;   
    //对结果的总结
    class QueryResult{ 
    public:
        //打印
        friend ostream &print(ostream &,const QueryResult&);
        //对结果进行整合
        QueryResult(string s,shared_ptr<set<line_no>> p,shared_ptr<vector<string>> f):sought(s),lines(p),file(f){ };
    private:
        //查询的单词
        string sought;
        //出现的行号
        shared_ptr<set<line_no>> lines;
        //输入的文件
        shared_ptr<vector<string>> file;
    };
    
    class TextQuery
    { 
    private:
        //输入文件
        shared_ptr<vector<string>> file;
        //每个单词到它所在行号的集合的映射
        map<string,shared_ptr<set<line_no>>> wm;
    public:
        //要查询的是文件
        TextQuery(ifstream &);
        //查询函数
        QueryResult query(const string &) const;
        ~TextQuery();
    };
    //次数>1 time要加s 
    string make_plural(size_t ctr,const string &word, const string &ending);
    //要查询的文件
    void runQueries(ifstream &infile);
    #endif

main.cpp

ifstream fs("E:\\code\\word.txt");
     runQueries(fs);

结果  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY3MjQwNA_size_16_color_FFFFFF_t_70 2]

[20210426133415866.png]: /images/20221022/a8e73b6ea8094538b48eee94cf18f401.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY3MjQwNA_size_16_color_FFFFFF_t_70]: /images/20221022/a9e63964c81a436988be648b9999b02c.png
[2021042614281889.png]: /images/20221022/b6e056309d4d411e83d240f94db20e30.png
[2021042615160023.png]: /images/20221022/1fa87b9adc1849b4a5ef072185f930f7.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY3MjQwNA_size_16_color_FFFFFF_t_70 1]: /images/20221022/35079772193349d0b669e4ed025b9fdd.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY3MjQwNA_size_16_color_FFFFFF_t_70 2]: /images/20221022/c3a77976786a42e796138cb0db957637.png