关键字new和delete可以重载

代码如下：

void test5() {

    Base *p1 = new Base;
    p1->a = 10;
    printf("0x%x\n", &(*p1));
    printf("%d\n", sizeof(*p1));
    
    delete p1;
}

这段代码可以用到关键字：new 和delete 关键字。但是貌似也可重写；具体入下：

class Base
{
public:
    Base();
    ~Base();
    void operator delete(void* const block, size_t const) {
        printf("%s", __FUNCSIG__);
    }

    void*  operator new(size_t const size) {
        printf("%s", __FUNCSIG__);
        return NULL;
    }
    int a;

private:

};

原来真的可以；
delete底层是这样的：

void __CRTDECL operator delete(void* const block) noexcept
{
0136C9E0  push        ebp  
0136C9E1  mov         ebp,esp  
    #ifdef _DEBUG
    _free_dbg(block, _UNKNOWN_BLOCK);
0136C9E3  push        0FFFFFFFFh  
    #ifdef _DEBUG
    _free_dbg(block, _UNKNOWN_BLOCK);
0136C9E5  mov         eax,dword ptr [block]  
0136C9E8  push        eax  
0136C9E9  call        __free_dbg (0136172Bh)  
0136C9EE  add         esp,8  
    #else
    free(block);
    #endif
}

居然用free,看来new是用malloc之流的C函数创建的；

那么来了解下new 、构造函数、析构函数、deletel的调用顺序吧。代码如下:

class Base
{
public:
    Base();
    ~Base();
    void operator delete(void* const block, size_t const) {
        printf("=====%d\n", sizeof(block));
        printf("%s\n", __FUNCSIG__);

        free(block);
    }

    void*  operator new(size_t const size) {
        printf("%s\n", __FUNCSIG__);
        void* ptr = malloc(size);
        memset(ptr, 0, size);
        return ptr;
    }
    int a;

private:

};

Base::Base()
{
    printf("%s\n", __FUNCSIG__);
}

Base::~Base()
{
    printf("%s\n", __FUNCSIG__);
}


void test5() {

    Base *p1 = new Base;
    p1->a = 10;
    printf("0x%x\n", &(*p1));
    printf("%d\n", sizeof(*p1));
    delete p1;
}



int main()
{
    test5();
    //Base p1=  test5();
    return EXIT_SUCCESS;
}

打印结果：

void *__cdecl Base::operator new(const unsigned int)
__thiscall Base::Base(void)
0x5e0260
4
__thiscall Base::~Base(void)
=====4
void __cdecl Base::operator delete(void *const ,const unsigned int)

。完事。
我手动实现了new 和delete函数