#include <windows.h>
#include <iostream>
using namespace std;
class A
{
public:
static A* Create()
{
if (m_IsAlreadyCreated)
return (A*)0;
else
{
return (A*)(operator new (sizeof(A)));
}
}
static void* operator new (size_t size)
{
if (m_IsAlreadyCreated)
return (void*)0;
if (size != sizeof(A))
{
/*********************************************
解决办法一:
void* pNew = 0;
pNew = ::operator new(size);//注意,这里不会调用类A的构造函数,所以我没有采纳,以后或许有更好的办法.
if (pNew)
{
m_IsAlreadyCreated = true;
}
return pNew;
**********************************************/
return (void*)0;
}
A* pA = (A*)::malloc(size);
if (pA)
{
pA->A::A();
}
return pA;
}
static void operator delete(void* pData,size_t size)
{
if (!pData || !m_IsAlreadyCreated)
return ;
if (size != sizeof(A))
{
/*********************************************
解决办法一:
::operator delete(pData);//注意,这里不会调用类A的析构函数,所以我没有采纳,以后或许有更好的办法.
m_IsAlreadyCreated = false;
**********************************************/
throw;/*暂时抛出异常*/
return ;
}
else
{
A* pA = (A*)pData;
pA->A::~A();
::free(pData);
}
}
void Delete()
{
if (m_IsAlreadyCreated)
operator delete(this,sizeof(A));
}
~A()
{
m_IsAlreadyCreated = false;
cout << "Destruction A" << endl;
}
private:
A()
{
m_IsAlreadyCreated = true;
cout << "Construction A" << endl;
}
A(A&){}
static bool m_IsAlreadyCreated;
};
bool A::m_IsAlreadyCreated = false;
int main()
{
//A a; //error;
//A* pa = new A; //error;
{
A* pA = (A*)(A::operator new(sizeof(A)));
pA->Delete();
}
{
A* pA = A::Create();
pA->Delete();
}
{
A* pA = (A*)(A::operator new(sizeof(A)));
A::operator delete(pA,sizeof(A));
}
{
A* pA = (A*)(A::operator new(sizeof(A)));
delete pA;
}
{
A* pA = (A*)(A::operator new(sizeof(A)));
A::operator delete(pA,sizeof(A)+sizeof(A));
}
return 0;
}