您可以将临时对象传递给通过引用获取变量的函数吗？

Question

I am having a problem understanding a compiler error.

The member function add() being called on an object named rolo takes a Card variable by reference:

class Card{
public:
    Card(string first,string last,string occupation,string address,string phoneNum);
};

class Rolodex{
public:
    void add(Card& card);
};

int main()
{
    Rolodex rolo;
    rolo.add(Card("Tony", "Hansen", "Writer", "12 E. St. NY, NY 33333", "555-9999"));
}

The compiler is giving me an error on this line:

rolo.add(Card("Tony", "Hansen", "Writer", "12 E. St. NY, NY 33333", "555-9999"));

Non-const lvalue reference to type 'Card' cannot bind to a temporary of type 'Card'.

I don't think that it is legal to call the method with a temporary object as argument. I think it is better if the following is done instead:

Card variable("Tony", "Hansen", "Writer", "12 E. St. NY, NY 33333", "555-9999");
rolo.add(variable);

Why is the error happening? Is there a way to fix it?

Answer 1

You can't bind a temporary to a non-const lvalue reference ( Card& card ). One solution is to pass it as a const lvalue reference instead:

void add(Card const & card);