get_tmp_dir

Gets the directory to use for temporary files.

On UNIX, this is taken from the `TMPDIR` environment variable. If the variable is not set, `P_tmpdir` is used, as defined by the system C library. Failing that, a hard-coded default of "/tmp" is returned.

On Windows, the `TEMP` environment variable is used, with the root directory of the Windows installation (eg: "C:\") used as a default.

The encoding of the returned string is system-defined. On Windows, it is always UTF-8. The return value is never null or the empty string.

Returns:

the directory to use for temporary files.