find - returns the offset of the first occurance of a substring, in a larger string. If it isn't found string::npos (typically 0xffffffff) is returned.
rfind - returns the offset of the last occurance of a substring, in a larger string. If it isn't found string::npos (typically 0xffffffff) is returned.
find_first_of - returns the index of the first character within the current string that matches any character in str
find_last_of - returns the index of the last character within the current string that matches any character in str
Sample code for find and rfind first_first_of, find_last_of
Sample code which creates the intersection of two sets, using the find_first_of function.