Stringstream - Convert an object to a string

Question

I have a complex object that I want to be able to pass into a std::ostringstream with the << operator just like a string or int. I want to give the ostringstream the object's unique id (int) and/or name (string). Is there an operator or method I can implement in my class to allow this to work?

Yes just overload the << operator - see stackoverflow.com/questions/4421706/operator-overloading — Martin Beckett
– Martin Beckett, Commented Jun 5, 2012 at 22:01
unique id in what context? In an instance of running process you could use it's memory address. — Ivarpoiss
– Ivarpoiss, Commented Jun 5, 2012 at 22:02
They are "Student" objects, for a class project. Each Student object has a name, id, address, and phone number, and are built from a txt file. — Marsh
– Marsh, Commented Jun 5, 2012 at 22:09
@MartinBeckett - overload << for my class, or for ostringstream? — Marsh
– Marsh, Commented Jun 5, 2012 at 22:10
@mouseas - for your class. Each class simply has a function that is called when you ask for '<<' which prints the values. It's just that for int/float/double etc they are built-in — Martin Beckett
– Martin Beckett, Commented Jun 5, 2012 at 22:11

bames53 · Accepted Answer · 2012-06-05 23:29:49Z

Define an operator overload in the same namespace as your class:

template<typename charT, typename traits> std::basic_ostream<charT, traits> & operator<< (std::basic_ostream<charT, traits> &lhs, Your_class const &rhs) { return lhs << rhs.id() << ' ' << rhs.name(); }

If the output function needs access to private members of your class then you can define it as a friend function:

class Your_class { int id; string name; template<typename charT, typename traits> friend std::basic_ostream<charT, traits> & operator<< (std::basic_ostream<charT, traits> &lhs, Your_class const &rhs) { return lhs << rhs.id << ' ' << rhs.name; } };

Note that this does not result in a member function, it's just a convenient way to declare and define a friend function at once.

The traits template parameter has a default value, so it can be skipped.

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