关于operator new及placement new,和相关的delete重载

最新推荐文章于 2025-07-14 22:37:56 发布

原创最新推荐文章于 2025-07-14 22:37:56 发布 · 393 阅读

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本文探讨了C++中自定义new和delete运算符的实现方法，包括placement new和数组new/delete等，并讨论了不同编译器下异常处理的区别。

class Fruit
{
   int no;
   double weight;
   char key;
public:
   void print() {   }
   virtual void process(){   }
};

class Apple: public Fruit
{
public:
     Apple():m_id(0)
     {
        cout<<"Apple default constructor,this="<<this<<" id="<<m_id<<endl;
     }
     Apple(int i):m_id(i)
     {
        cout<<"Apple constructor,this="<<this<<" id="<<m_id<<endl;
        throw bad();
     }
    ~ Apple()
    {
        cout<<"Apple destructor,this="<<this<<" id="<<m_id<<endl;
    }
    void *operator new(size_t size)
    {
        Apple* p=(Apple*)malloc(size);
        cout<<"operator new:"<<size<<endl;
        return p;
    }
    void *operator new[](size_t size)
    {
        Apple* p=(Apple*)malloc(size);
        cout<<"operator new[]:"<<size<<endl;
        return p;
    }
    void operator delete(void* v,size_t size)
    {
        cout<<"operator delete:"<<size<<endl;
        free(v);
    }
    void operator delete[](void* v,size_t size)
    {
        cout<<"operator delete[]:"<<size<<endl;
        free(v);
    }
    /////////////////////////
    void* operator new(size_t size,void *start)
    {
        return start;
    }
    void* operator new(size_t size,long extra)
    {
        return malloc(size+extra);
    }
    void* operator new(size_t size,long extra,char init)
    {
        return malloc(size+extra);
    }
    // void* operator new(long extra,char init)
    // {}

    void operator delete(void*,void*)
    {
        cout<<"operator delete(void*,void*)"<<endl;
    }
    void operator delete(void*,long)
    {
        cout<<"operator delete(void*,long)"<<endl;
    }
    void operator delete(void*,long,char)
    {
        cout<<"operator delete(void*,long,char)"<<endl;
    }
private:
    int m_id;
    long m_data;
    string m_str;
    int size;
    char type;
public:
   void save() {   }
   virtual void process(){   }
};

测试 operator new及operator placement new,还有相关的new[],delete,delete[]等,其中 palcement的delete是用来处理异常的,只有当构造函数抛出异常的时候才调用,并且不同编译器有可能处理不一样,gcc下是调用的,vc下是未调用的直接抛出了异常并终止了程序(未验证)