Using overloaded operators on pointers

Question

Hi,

I overloaded the << operator of a class. How do I have to overload the operator if I want to use it on pointers, like the following?

class A {
    std::string operator<<(std::string&);
}

aInst << "This works";
aPointer << "This doesnt work";
aPointer->operator<<("Whereas this works but is useless");

I hope you can help me.

heinrich

Answer 1

You need to dereference the pointer first.

A *ptr = new A();
(*ptr) << "Something";

The only other way is the way you described above

Edit: Andre's solution below is workable as well, but like he said it may not be a good idea.

Answer 2

You cannot do that. Operator functions are only considered for operands that have enumeration or class types among them.

You after all shift a pointer, but not a class. You need to explicitly say that you want to shift into a class object by dereferencing the pointer first.

Answer 3

Normally there is no good reason doing that, because semantically operator << return reference to stream object. And technically you basically can't do that.

Answer 4

First off, to stick with standard conventions, your operator<< should be declared like this:

class A {
    A& operator<<(const std::string&);
};

Now, technically, you could achiever part of what you want by implementing the following global function:

A * operator<< ( A * a, const std::string& s ) { (*a) << s; return a; }

This would allow statements such as:

string s = "this will be printed."; aPointer << s;
aPointer << string("this will be printed");

However, you won't be able to write the following:

aPointer << "this will not compile.";

In any case, writing such an operator would be confusing, at best. You should live with the more simple syntax of

(*aPointer) << "this will be printed.";

and write code that sticks to established conventions to allow others (and yourself, in a few weeks) to read your code.