unitynewbyte释放_C++幕后故事（九）我们来new个对象

/****************************************************************************
**
** Copyright (C) 2019 635672377&＃64;qq.com
** All rights reserved.
**
****************************************************************************//*测试对象的new、delete&＃xff0c;在VS2017更容易观察
*/
#ifndef obj_new_delete_h
#define obj_new_delete_h#include
#include
#include using std::cout;
using std::endl;namespace obj_new_delete
{class Obj
{
public:Obj():mCount(0) { cout <<"Obj ctor" <};void test_new_obj()
{Obj *obj &＃61; new Obj();
delete obj;
}
}
#endif // obj_new_delete_h


; Obj *obj &＃61; new Obj();
00DE2C47 push 4
00DE2C49 call operator new (0DE141Ah)
00DE2C4E add esp,4
00DE2C51 mov dword ptr [ebp-0ECh],eax
00DE2C57 mov dword ptr [ebp-4],0
00DE2C5E cmp dword ptr [ebp-0ECh],0
00DE2C65 je obj_new_delete::test_new_obj&＃43;7Ah (0DE2C7Ah)
00DE2C67 mov ecx,dword ptr [ebp-0ECh]
; 调用对象的构造函数
00DE2C6D call obj_new_delete::Obj::Obj (0DE1456h)

void* __CRTDECL operator new(size_t const size)
{for (;;)
{// 这个有个小技巧&＃xff0c;控制变量的作用域&＃xff0c;没必要让其他对象见到这个变量的作用域if (void* const block &＃61; malloc(size)){return block;}// _callnew内部会调用new_handler&＃xff0c;
// 返回值为0表示new_handler类型函数为null&＃xff0c;这样就不会调用new_handler类型函数&＃xff0c;
// 抛出两个其中一个的异常&＃xff0c;大小异常&＃xff0c;内存分配异常。// 否则就会调用设置的new_handler类型函数if (_callnewh(size) &＃61;&＃61; 0){if (size &＃61;&＃61; SIZE_MAX){__scrt_throw_std_bad_array_new_length();}else{__scrt_throw_std_bad_alloc();}}// The new handler was successful; try to allocate again...
}
}


// 重载global new
void * operator new(size_t const size)
{return malloc(size);
}// 重载global delete
void operator delete(void *head)
{return free(head);
}class Obj
{
public:Obj():mCount(0) { cout <<"Obj ctor" <(::operator new(size));}// 重载局部deletevoid operator delete(void *head){return ::operator delete(head);
}private:int mCount;
};


void test_placement_new()
{char *buff &＃61; new char[sizeof(Obj)];Obj *ojb &＃61; new(buff)Obj();
}


; char *buff &＃61; new char[sizeof(Obj)];
00892558 push 4
0089255A call operator new[] (0891118h)
0089255F add esp,4 ; eax中保存了new char返回的首地址
00892562 mov dword ptr [ebp-0E0h],eax
00892568 mov eax,dword ptr [ebp-0E0h]
0089256E mov dword ptr [buff],eax ; Obj *ojb &＃61; new(buff)Obj();; 将eax中的首地址作为参数传递进去
00892571 mov eax,dword ptr [buff]
00892574 push eax ; Obj对象的大小
00892575 push 4
00892577 call operator new (0891550h)
0089257C add esp,8
0089257F mov dword ptr [ebp-0ECh],eax
00892585 mov ecx,dword ptr [ebp-0ECh] ; 调用Obj的构造函数
0089258B call obj_new_delete::Obj::Obj (0891456h)
00892590 mov dword ptr [ojb],eax

_Ret_notnull_ _Post_writable_byte_size_(_Size) _Post_satisfies_(return &＃61;&＃61; _Where)
inline void* __CRTDECL operator new(size_t _Size, _Writable_bytes_(_Size) void* _Where) noexcept
{(void)_Size;return _Where;
}


template
inline void construct(T1* p, const T2& value) {new (p) T1(value);
}// vector push_back函数
void push_back(const T& x) {if (finish !&＃61; end_of_storage) {construct(finish, x); &＃43;&＃43;finish; }else insert_aux(end(), x);
}


class Obj
{
public:Obj():mCount(0) { cout <<"Obj ctor" <}// 重载placement deletevoid operator delete(void *buff, void *address, long extra){return ::operator delete(buff, address);}
private:int mCount;
};void test_placement_new()
{char *buff &＃61; new char[sizeof(Obj)];// Obj *ojb &＃61; new(std::cerr)Obj();Obj *obj &＃61; new(buff)Obj();obj->~Obj();
Obj *obj_1 &＃61; new(buff, 123456)Obj();obj_1->~Obj();delete buff;// 打印结果// void *operator new(size_t size, void *address) version// Obj ctor// ~Obj ctor// void *operator new(size_t size, void *address, long extra) version extra:123456 // Obj ctor// ~Obj ctor
}


void new_exception_handler()
{cout <<"memory cout..." <}void test_new_obj()
{// 测试new_set_handlerstd::new_handler old_handler &＃61; std::set_new_handler(new_exception_handler);while (true) {new int[100000000ul];}cout <<"end..." <}