[fs.op.canonical]

path filesystem::canonical(const path& p);
path filesystem::canonical(const path& p, error_code& ec);

Effects: Converts p to an absolute path that has no symbolic link, dot, or dot-dot elements in its pathname in the generic format.

Returns: A path that refers to the same file system object as absolute(p).

The signature with argument ec returns path() if an error occurs.

Remarks: !exists(p) is an error.

31 Input/output library [input.output]