bool create_directories(const path& p);
bool create_directories(const path& p, error_code& ec) noexcept;
Effects: Establishes the postcondition by calling create_directory() for any element of p that does not exist.
Postconditions: is_directory(p).
Returns: true if a new directory was created, otherwise false. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
Complexity: Ο(n) where n is the number of elements of p that do not exist.