path canonical(const path& p, const path& base = current_path());
path canonical(const path& p, error_code& ec);
path canonical(const path& p, const path& base, error_code& ec);
Effects: Converts p, which must exist, to an absolute path that has no symbolic link, ".", or ".." elements.
Returns: A path that refers to the same file system object as absolute(p, base). For the overload without a base argument, base is current_path(). Signatures with argument ec return path() if an error occurs.
Throws: As specified in [fs.err.report].
Remarks: !exists(p) is an error.