You mean, how long is a piece of string?
After thinking about your query, the only good idea I had was to take something like a large open source codebase and write a program to search for string/char declarations. It'd probably be faster just to try your idea and see whether it helps or not :-/
Oh, and nothing about that on Alpha, sorry. I did ask it 'how long is a string' for fun, and it suggested that the length of a given random string is 12. And who am I to argue?