Returning a reference can work?

Question

I used to think returning a reference is bad as our returned reference will refer to some garbage value. But this code works (matrix is a class):

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Answer 1

This is safe up to a point, but very dangerous. The returned reference can't dangle, but if client code keeps it around, at some future point, the client is in for a big surprise, as his value suddenly changes to a new return value. And if you call get_matrix_temp more than max_matrix_temp times in a single expression, you're going to end up overwriting data as well.

In the days before std::string, in code using printf, I used this technique for returning conversions of user defined types, where a "%s" specifier was used, and the argument was a call to a formatting function. Again, max_matrix_temp was the weak point: a single printf which formatted more instances of my type would output wrong data. It was a bad idea then, and it's a worse idea now.