Bugs in my code, help!!

[Al-Burak]

This is not a question where the source code is important, it is not
important at all. So don't expect to find answers to my questions in
the code; the answers will be in how the class interacts with the rest
of the program and/or how GCC can help me resolve my problem.

Having said that, I have a class called 'Person', and a class
called 'io_base', the purpose of 'io_base' is to implement file
input and output in a uniform manner for all my classes. All the user
of this class has to do is ask 'io_base' to open a file and then,
via the use of inserters and extractors, input or output data to and
from the file, as simple as that. The class takes care of managing the
stream state as well as the integrity of the data and if there are any
problems, an exception is thrown testifying to the cause of the error.
Neat, he!
Now, class 'Person', is one of the classes being managed by
'io_base' which has been declared and implanted in the same manner
as the other classes in my library.
However, when compiling, or attempting to compile class 'Person' as
part of the rest of my library I get an error telling me that there is
a previous definition of 'class Person'. But this only happens if I
try to compile the entire library with it, library that is in source
code format still, as opposed of being in 'dll' or 'so' format.
This is a bug, obviously, and I will eventually find the bug; however
my question is, does anyone here know a better way to find this kind of
errors than to go line by line looking for the bug? Is there a
parameter in GCC that I can use so that the compiler is more specific,
or become more elaborate in what/where the error is?

Any help towards the solution of my problem will be most appreciated.

TIA.