cpp/experimental/fs/absolute

@1@ Returns absolute path of relative to  according to the following rules:
 * If has both root name and root directory (e.g., then the path is returned, unmodified.
 * If has a root name not followed by a root directory (e.g. ), then  is inserted between 's root name and the remainder of . Formally,  is returned,
 * If has no root name, but has a root directory (e.g.  on a POSIX system or  on Windows, then the root name of, if it has one, is prepended to  (on a POSIX system,  is not modified, on a Windows system,  becomes . Formally,  is returned.
 * If has no root name and no root directory (e.g., then the entire  is prepended to . Formally,  is returned.

@2@ Obtains the absolute path that identifies the file that the OS file opening API would access given the pathname. On POSIX systems, this is equivalent to with the default. On Windows systems, each logical drive has its own current working directory, and so if is not already absolute and has a root name component (e.g., that drive's current working directory is used, which may have been set by an earlier executed program.

Return value
Returns an absolute (although not necessarily canonical) path formed by combining and  as described above.