C++内存管理10 重载示例

#include 
#include 
#include 
namespace jj06
{
using namespace std;
class Foo
{
public:
  int _id;
  long _data;
  string _str;
  
public:
  	static void* operator new(size_t size);
  	static void  operator delete(void* deadObject, size_t size);
  	static void* operator new[](size_t size);
  	static void  operator delete[](void* deadObject, size_t size);	  	  
  
  Foo() : _id(0)      { cout << "default ctor. this="  << this << " id=" << _id << endl;  }
  Foo(int i) : _id(i) { cout << "ctor. this="  << this << " id=" << _id << endl;  }
  //virtual 
  ~Foo()              { cout << "dtor. this="  << this << " id=" << _id << endl;  }
  
  //不加 virtual dtor, sizeof = 12, new Foo[5] => operator new[]() 的 size 參數是 64, 
  //加了 virtual dtor, sizeof = 16, new Foo[5] => operator new[]() 的 size 參數是 84, 
  //上述二例，多出來的 4 可能就是個 size_t 欄位用來放置 array size. 
};

void* Foo::operator new(size_t size)
{
  	Foo* p = (Foo*)malloc(size);  
	cout << "Foo::operator new(), size=" << size << "\t  return: " << p << endl;  	

  	return p;
}

void Foo::operator delete(void* pdead, size_t size)
{
	cout << "Foo::operator delete(), pdead= " << pdead << "  size= " << size << endl;
	free(pdead);
}

void* Foo::operator new[](size_t size)
{
  	Foo* p = (Foo*)malloc(size);  //crash, 問題可能出在這兒 
	cout << "Foo::operator new[](), size=" << size << "\t  return: " << p << endl;  
	
  	return p;
}

void Foo::operator delete[](void* pdead, size_t size)
{
	cout << "Foo::operator delete[](), pdead= " << pdead << "  size= " << size << endl;
	
	free(pdead);
}
	
//-------------	
void test_overload_operator_new_and_array_new() 
{	
	cout << "\ntest_overload_operator_new_and_array_new().......... \n";		
	
	cout << "sizeof(Foo)= " << sizeof(Foo) << endl;
	
	{	
    Foo* p = new Foo(7);
    delete p;
    
    Foo* pArray = new Foo[5];	//無法給 array elements 以 initializer 
    delete [] pArray;	
	}
	
	{	    
	cout << "testing global expression ::new and ::new[] \n";
	// 這會繞過 overloaded new(), delete(), new[](), delete[]() 
	// 但當然 ctor, dtor 都會被正常呼叫.  
	
    Foo* p = ::new Foo(7);
    ::delete p;
    
    Foo* pArray = ::new Foo[5];	
    ::delete [] pArray;
	}
}
} //namespace
int main(){
    jj06::test_overload_operator_new_and_array_new();
    return 0;
}

运行结果：