Couple of things:

1. If toString() is supposed to return a string object, then you probably shouldn't be taking the address of said object in order to print it out via an ostream.

2. You're taking the address of a temporary returned from a function. The warning is there because its attempting to tell you that the address is to a temporary object whose lifetime ends in the very near future.

3. I suspect your code is doing what you expect it to do.

now how to get the name?

Get the name of what exactly? You have a bunch of airports, are you trying to get the name of the first one? All of them?

The code is not mine (gpl) ...

Which code isn't yours? The Airport class, or perhaps QString?

... but I suppose that's what toString should be used for?

It depends on the codebase. Most I've come across treat toString() as a debugging tool, so the content is a convenient programmer's description of the object, but not necessarily suitable for an end user. But it really is down to the project conventions.

For example, an Aiport class might have a toString() that returns a compound string containing the human name and the airport code, e.g. "London Heathrow Airport [LHR]". In a database system, it might also include identifiers. Clients that wish to render a representation of the Airport would use member functions such as name() or getName(), code() or getCode() to build a U.I. suitable for end users. For instance, a HTML based U.I. might place tags around the name or code to emphasise or de-emphasise as necessary.

I think it is clearer to use explicit member functions to render objects, rather than rely on the programmers memory that Airport::toString() returns the name, for example.