To compute the size of a directory, we have to iterate through all the files and sum the size of individual files.
filesystem::recursive_directory_iterator is an iterator from the filesystem library that allows iterating all the entries of a directory in a recursive manner. It has various constructors, some of them taking a value of the type filesystem::directory_options that indicates whether symbolic links should be followed or not. The general purpose std::accumulate() algorithm can be used to sum together the file sizes. Since the total size of a directory could exceed 2 GB, you should not use int or long, but unsigned long long for the sum type. The following function shows a possible implementation ...
