I can't see to wrap my head arround the meaning of this error.
Its becouse im converting integer functions to character functions.

src/dataio.cpp: In function ‘char* getName(char)’:
src/dataio.cpp:118:17: error: invalid conversion from ‘char’ to ‘char*’ [-fpermissive]
     readUser(uid);
                 ^
src/dataio.cpp:60:6: note: initializing argument 1 of ‘void readUser(char*)’
 void readUser(char* uid)  ///Reads users from data directory

The error means that the readUser function expects an argument of type char*, but you're giving it a char.