There is nothing intrinsically wrong with your code. i.e. in a stand alone test env. it works.
The error you are getting comes from your library matrixOptLibrary.h. There are any number of reasons that this code is going to break it. (a) the using namespace std; ,
and more likely (b) that your typedef is in a include file and it is not in a namespace, and it is above an #include "matrixOptLibrary.h".
If you can post a small complete test code that produces the error, we will have another look. Otherwise pay particular attention to your .h files, particularly if you also have #include lines in them.
I am working creating a fully encapsulated, homogeneous singly linked data structure. The Listing class and SinglyLinkedList class that are part of the whole application compile fine, but the problem ...