Hi Claude,
Remember if you have access to a recent C++ compiler, you can use regular expressions! If not, you can still use the Boost alternatives: Boost.Regex or Boost.Xpressive.
I'm assuming that you know beforehand the number of "quoted sub-strings", because otherwise, regular expressions are not so useful, and people often recommend Boost.Spirit, which is too complex for this simple task.
About the trim operation you want to do in the outside parts, remember Boost.StringAlgo has it for you. ;-)
Good luck,
Júlio.