std::experimental::filesystem::path::is_absolute,is_relative
Min standard notice:
Checks whether the path is absolute or relative. An absolute path is such that the elements of root_path() uniquely identify a file system location. The first version returns true if the path is absolute, false otherwise; the second version the other way round.
# Declarations
bool is_absolute() const;
(filesystem TS)
bool is_relative() const;
(filesystem TS)