[C++知识库]16.C++ 对象的生成原理

1.new operator和delete operator

? ? //程序调用new operator做了下面两件事
? ? //1.用操作符operator new开辟空间
? ? //2.调用构造函数
? ? //程序调用delete operator做了下面两件事
? ? //1.调用析构函数
? ? //2.operator delete释放p所指向的空间

#include <iostream>
using namespace std;
class Int {
private:
    int data;
public:
    Int(int i):data(i) {
        cout << "构造对象"<< data << endl;
    }
    ~Int() {
        cout << "析构对象" << data << endl;
    }
};

int main()
{
    //Int i(10086);//这是静态开辟，编译器在编译的时候就知道这个类开辟多少空间
    Int* p = new Int(10086);
    delete p;
    //程序调用new operator做了下面两件事
    //1.用操作符operator new开辟空间
    //2.调用构造函数
    //程序调用delete operator做了下面两件事
    //1.调用析构函数
    //2.operator delete释放p所指向的空间

    return 0;
}

2.operator new 和operator delete

#include <iostream>
using namespace std;

class Int {
private:
    int data;
public:
    Int(int i):data(i) {
        cout << "构造对象"<< data << endl;
    }
    ~Int() {
        cout << "析构对象" << data << endl;
    }
};

//====================================================================
void* operator new(size_t size)//size_t:unsigned int
{
    cout << "开辟内存" << size <<endl;
    void* p = malloc(size);
    return p;

}

void operator delete(void* p)
{
    cout << "释放内存" << p <<endl;
    free(p);
}
//====================================================================

int main()
{
    Int* q =new Int(1);//new操作符内部会自动计算Int类大小，然后把值赋值给size_t size
    delete q;

    //下面是实现过程
    Int* p = (Int*)operator new(sizeof(Int));//开辟一个类大小的内存
    new(p)Int(2);//把2放到开辟的空间中
    p->~Int();//调用析构函数
    operator delete (p);//释放内存空间
    return 0;
}
//====================================================================

ee

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