Parsing user-defined types

I'm having trouble seeing how to handle user-defined types without lots 
of feedback from the parser to the lexer. For example, consider a C-like 
language with a struct declaration:

foo() {
   struct a {...};  // type defn
   struct a b;      // declare object 'b' of user-defined type 'a'
}

this is easy to parse, but if you add a typedef, or go to C++, you can 
have code that looks like this:

foo() {
   struct a {...};
   a b;
}

With a simple flex/bison setup this is likely to lead to a lot of 
conflicts. So how do you handle this? Do you just work through the 
conflicts, if possible, or is this a job for a hand-coded lexer, which 
can be told about new types at runtime?

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