Well, the opposite thing to do is to wrap relevant portions of your C++ code with extern C{}, which won't always work, especially if you're using overloading.

My guess is that you're trying to call C++ functions from C and the C object file is expecting to see myfunc() and the C++ object file is providing gnu_int_int_myfunc() or some such nonsense.

Of course, I could be completely off base.