手撕shared_ptr智能指针

Posted 2023-02-09 每天告诉自己要努力

#include <bits/stdc++.h>
using namespace std;

class control_block 
private:
    atomic<size_t> cnt;
public:
    control_block() : cnt(0) 
    void add()  cnt++; 
    void sub()  cnt--; 
    size_t getCnt()  return cnt; 
;


template<class T>
class mySharedPtr 
private:
    T* m_ptr;
    control_block* ctrl_blk;
    void release() 
        if (ctrl_blk != nullptr) 
            ctrl_blk->sub();
            if (ctrl_blk->getCnt() == 0) 
                delete m_ptr;
                delete ctrl_blk;
                m_ptr = nullptr;
                ctrl_blk = nullptr;
            
        
    
public:
    mySharedPtr() : m_ptr(nullptr), ctrl_blk(new control_block()) 
    explicit mySharedPtr(T* ptr) : m_ptr(ptr) 
        ctrl_blk = new control_block();
        ctrl_blk->add();
    
    mySharedPtr(const mySharedPtr& ptr) 
        ctrl_blk = ptr.ctrl_blk;
        m_ptr = ptr.m_ptr;
        ctrl_blk->add();
    
    mySharedPtr(mySharedPtr&& ptr) 
        m_ptr = ptr.m_ptr;
        ctrl_blk = ptr.ctrl_blk;
        ptr.m_ptr = nullptr;
        ptr.ctrl_blk = nullptr;
    
    mySharedPtr& operator=(const mySharedPtr& ptr) 
        if (this == &ptr) return *this;
        release();
        m_ptr = ptr.m_ptr;
        ctrl_blk = ptr.ctrl_blk;
        ctrl_blk->add();
        return *this;
    
    ~mySharedPtr() 
        release();
    
    T* operator->() 
        return m_ptr;
    
    T& operator*() 
        return *m_ptr;
    
    size_t use_count() 
        return ctrl_blk->getCnt();
    
;

int main () 
    mySharedPtr<string> p1(new string("hello world"));
    cout << *p1 << " " << p1.use_count() << endl;

    mySharedPtr<string> p2(p1);
    cout << *p2 << " " << p2.use_count() << endl;

    mySharedPtr<string> p3(new string("hello"));
    p2 = p3;
    cout << *p2 << " " << p2.use_count() << endl; //hello 2
    cout << *p1 << " " << p1.use_count() << endl; //hello world 1

    system("pause");
    return 0;