class A1{
public:
A1(){}
A1(const A1& rhs){}
void foo() {std::cout<<"Hello";}
};
class A2: public A1{
public:
A2(){}
A2(const A2& rhs){}
void foo1(A1&rhs){rhs.foo();}
void foo2(A1 a1){a1.foo();}
};
int main()
{
A2 a2;
A1 a1(a2);
a2.foo1(a1);
a2.foo2(a1);
}
How many times are the A1's copy constructor invoked? How many times are the A2's copy constructor invoked?
Could anybody can teach me this? thanks!
It's much easier to talk about code that doesn't reuse variable names everywhere.
The copy constructor for A1 is called twice, and for A2 not at all.
class A1{
public:
A1(){}
A1(const A1& rhs){}
void foo() {std::cout<<"Hello";}
};
class A2: public A1{
public:
A2(){}
A2(const A2& rhs){}
void foo1(A1& a1byref){a1byref.foo();}
void foo2(A1 a1byval){a1byval.foo();}
};
int main()
{
A2 a2;
A1 a1(a2); // calls A1 copy constructor
a2.foo1(a1);
a2.foo2(a1); // calls A1 copy constructor
}
Modifying your code slightly for more explicit output, I have:
#include <iostream>
class A1{
public:
A1(){}
A1(const A1& rhs)
{ std::cout << "A1::copy_ctor\n"; }
void foo()
{ std::cout << "A1::foo\n"; }
};
class A2: public A1{
public:
A2(){}
A2(const A2& rhs){}
void foo1(A1&rhs)
{
std::cout << "A2::foo1\n";
rhs.foo();
}
void foo2(A1 a1)
{
std::cout << "A2::foo2\n";
a1.foo();
}
};
int main()
{
A2 a2;
A1 a1(a2);
a2.foo1(a1);
a2.foo2(a1);
}
Which using Xcode 3.2.5 yields:
A1::copy_ctor
A2::foo1
A1::foo
A1::copy_ctor
A2::foo2
A1::foo
cout << "in A1's ctor" << endl;in the constructors and run the code to see for yourself.static int i = 0; std::cout << ++i << "th time in A1" << std::endl;