O_RDWR is used by very low-level C _open() function. Most programmers today use higher-level FILE* functions in C or fstream c++ class. But if you read this link you will see that O_RDWR is NOT one of the pmode flags -- pmode refers to permissions and is useful only when creating a new file.
i am currently in a file structure class and my teach teaches me the basic of C++ the book talks about unix and C so it is super confusing. And the books questions are in C++. Anyone know any basic link on file structures?
Most of the stuff you seen in your textbook will also probably apply to Vista. The major difference is in the include files. If you look towards the bottom of that link I posted you will find the include files you need and an example C program. It illustrates how to call _open() two ways: both with and without the pmode parameter.