#Wiki For You
I polished and updated my Wiki on Forward Declaration, just forward declare your character class in your inventory class
#Solution For You in Exact Detail
include your inventory class at the top of your character class
then you should #include your character class only in the .cpp file of your inventory class, avoid trying to access your character class in your inventory .h, You use forward declaration to include a pointer to your character class in your inventory .h, but you dont access its vars in the .h, only in the .cpp
#Summary
inventory class .h → forward declares character class (see wiki)
inventory class. cpp → now you can #include character class and actually access its functions and vars
character class .h → #include your inventory class, use inventory however you like in .h or .cpp
#Wiki Link
UE4 Forward Declaration
Rama
PS: dont mess with the UE4 auto-generated classes files, just do the above, you should make edits only to inventory and character classes at your project level.