TRUE if the given
file_name is an absolute file name.
Note that this is a somewhat vague concept on Windows.
On POSIX systems, an absolute file name is well-defined. It always starts from the single root directory. For example “/usr/local”.
On Windows, the concepts of current drive and drive-specific current directory introduce vagueness. This function interprets as an absolute file name one that either begins with a directory separator such as “\Users\tml” or begins with the root on a drive, for example “C:\Windows”. The first case also includes UNC paths such as “\myserver\docs\foo”. In all cases, either slashes or backslashes are accepted.
Note that a file name relative to the current drive root does not truly specify a file uniquely over time and across processes, as the current drive is a per-process value and can be changed.
File names relative the current directory on some specific drive,
such as “D:foo/bar”, are not interpreted as absolute by this
function, but they obviously are not relative to the normal current
directory as returned by
either. Such paths should be avoided, or need to be handled using
A file name.
The data is owned by the caller of the function. The value is a file system path, using the OS encoding.