The type openmode is a bitmask type ([bitmask.types]). It contains the elements indicated in Table [tab:iostreams.openmode.effects].
| Element | Effect(s) if set |
| app | seek to end before each write |
| ate | open and seek to end immediately after opening |
| binary | perform input and output in binary mode (as opposed to text mode) |
| in | open for input |
| out | open for output |
| trunc | truncate an existing stream when opening |