Explode string by pairs with regex

I receive a string that can have different formats:

22
44xx
44xx33yy
44xx33yy22

And I need to explode this line to:

line4[0]= { 44, "xx" }
line4[1]= { 33, "yy" }
line4[2]= { 22, "" }

Or in the reverse order but I don't known where to start.
Maybe with boost::regex.
Some one have a way or sample for me?