Don't have two identical typedef in different header files.

Only have one typedef <type> <typename>

And it's ok if many C files sees a extern <typename> <variablename> even if that C file will not make use of the variable. The part of the code that really allocates the variable may also see an extern statement for the variable. That is actually good, since that gives the compiler a chance to verify that all your extern statements are correct, and doesn't say a different data type.