| Function | Classification | Cancel | ISR | Signal | Thread |
|---|---|---|---|---|---|
| offsetof() | ANSI POSIX 1003.1 | No | Yes | Yes | Yes |
| open() | POSIX 1003.1 | Yes | No | Yes | Yes |
| open64() | Large-file support | Yes | No | Yes | Yes |
| opendir() | POSIX 1003.1 | Yes | No | No | Yes |
| openfd() | QNX Neutrino | Yes | No | Yes | Yes |
| openlog() | POSIX 1003.1 | Yes | No | No | Yes |
| openpty() | Unix | Yes | No | Yes | Yes |
| out8() | QNX Neutrino | No | Yes | Yes | Yes |
| out8s() | QNX Neutrino | No | Yes | Yes | Yes |
| out16() | QNX Neutrino | No | Yes | Yes | Yes |
| outbe16() | QNX Neutrino | No | Yes | Yes | Yes |
| outle16() | QNX Neutrino | No | Yes | Yes | Yes |
| out16s() | QNX Neutrino | No | Yes | Yes | Yes |
| out32() | QNX Neutrino | No | Yes | Yes | Yes |
| outbe32() | QNX Neutrino | No | Yes | Yes | Yes |
| outle32() | QNX Neutrino | No | Yes | Yes | Yes |
| out32s() | QNX Neutrino | No | Yes | Yes | Yes |