一道C++笔试题：设计一个只能在堆内存上实例化的类和一个只能在栈内存上实例化的类
只能在堆内存上实例化的类：将析构函数定义为private，在栈上不能自动调用析构函数，只能手动调用。也可以将构造函数定义为private，但这样需要手动写一个函数实现对象的构造。
只能在栈内存上实例化的类：将函数operator new和operator delete定义为private，这样使用new操作符创建对象时候，无法调用operator new，delete销毁对象也无法调用operator delete。
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#include <iostream>
using namespace std;
//只能在堆内存上实例化的类
class CHeapOnly
{
public:
CHeapOnly()
{
cout << "Constructor of CHeapOnly!" << endl;
}
void Destroy() const
{
delete this;
}
private:
~CHeapOnly()
{
cout << "Destructor of CHeapOnly!" << endl;
}
};
//只能在栈内存上实例化的类，就是不能使用new来构造类，把operator new私有化
class CStackOnly
{
public:
CStackOnly()
{
cout << "Constructor of CStackOnly!" << endl;
}
~CStackOnly()
{
cout << "Destrucotr of CStackOnly!" << endl;
}
private:
void* operator new(size_t size)
{
}
void operator delete(void * ptr)
{
}
};
int main()
{
//use of CHeapOnly
CHeapOnly* pHeap = new CHeapOnly;
pHeap->Destroy();
//error use of CHeapOnly
//CHeapOnly objHeap;
//use of CStackOnly
CStackOnly objStack;
//error use of CStackOnly
//CStackOnly* pStack = new CStackOnly;
return 0;
} |
下面一个类也只能在堆内存上生成，将构造函数和析构函数都定义为private，但是可以通过类的static函数创建对象，不过这个对象是不能被继承的。
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#include <iostream>
using namespace std;
//只能在堆内存上实例化的类
class FinalClass
{
public :
static FinalClass* GetInstance()
{
cout<<"Constructor of the class"<<endl;
return new FinalClass;
}
static void DeleteInstance(FinalClass* pInstance)
{
cout<<"Destructor of the class"<<endl;
delete pInstance;
pInstance = 0;
}
private :
FinalClass() {}
~FinalClass() {}
};
int main()
{
//use of CHeapOnly
FinalClass* fc = FinalClass::GetInstance();
FinalClass::DeleteInstance(fc);
return 0;
} |
