overloaded operator << on ofstream concatenation problems

Question

I have the following code:

struct simple
{
    simple (int a1, int a2) : member1(a1), member2(a2) {}
    int member1;
    int member2;
};

std::ofstream &         


        

Answer 1

On the line :

f << "label: " << s;

Because the first call to operator<< returns a std::ostream &, the second fails to compile : the left operand to the operator is not of type std::ofstream anymore and your overload is not found.

You should really use the second signature, as I see no reason for restricting your type to be outputted to std::ofstream.