filesystem_error(const string& what_arg, error_code ec);
filesystem_error(const string& what_arg, const path& p1, error_code ec);
filesystem_error(const string& what_arg, const path& p1, const path& p2, error_code ec);
const path& path1() const noexcept;
const path& path2() const noexcept;
const char* what() const noexcept override;