You would use the File class to manipulate the operating system files. This class is an imitation of Java's File class and will be very useful in C++ programming. Using this File class in C++ you can do if file exists() ?, if directory exists() ?, file length() and other functions.
Note that these classes has some great functionality not supported in The Standard C++ Library, but don't confuse them with fstreams(iostreams), which is the way you should perform many other operations on files.