学步园

#include  
using namespace std;
class base { 
public: 
	virtual int foo( int ival = 1024 ) { 
		cout << "base::foo() -- ival: " << ival << endl; 
		return ival; 
	} 
	// ... 
}; 

class derived : public base { 
public: 
	int foo( int ival = 2048 ) { 
		cout << "derived::foo() -- ival: " << ival << endl; 
		return ival; 
	} 
	// ... 
}; 
//======================================================================
// 证明了一点,virtual带缺省参数时,缺省参数和指针或引用对象类型绑定
// 也就是说基类指针或引用调用的是派生类中的函数,但是缺省参数是从基类
// 继承了过来,而派生类指针或引用调用的是自身的虚函数,缺省参数是本身的
//======================================================================
int main() 
{ 
	derived obj;
	derived *pd = &obj; //new derived; 
	base *pb = pd; 
	
	int val = pb->foo(); 
	cout << "main() : val through base: " 
		<< val << endl; 
	
	val = pd->foo(); 
	cout << "main() : val through derived: " 
		<< val << endl; 
	return 0;
}