• C++11 is the ISO C++ standard ratified in 2011. The previous standard is often referred to as C++98 or C++03; the differences between C++98 and C++03 are so few and so technical that they ought not concern users. C++14 is the informal name for a recent revision of the C++ standard. It is intended to be a small extension over C++11, featuring mainly bug fixes and small improvements.
• Differences between a class and a struct in C++ are that structs have default public members and bases and classes have default private members and bases. Both classes and structs can have a mixture of public and private members, can use inheritance, and can have member functions. Classes create a namespace that also encapsulate the functions for manipulating its data elements. Classes may not be used when interfacing with C, because C does not have a concept of classes.

Lets consider your /usr/local/lib/libYARP_OS.a. What you can do is, have -L/usr/local/lib/ in your makefile as one of the variables. And then you can have -lYARP_SO appended to the LDLIBS.

-L is for path to the lib and -l is the lib name here libYARP_OS.a will be passed as -lYARP_OS. On command line you would do something like: gcc -o main main.c -L/usr/local/lib/ -lYARP_SO. This should give you an idea.