how can t do than is appand? about memmap2-rs

[adamreichold]

The call to m_mut.deref_mut() produces a mutable slice &mut [u8] covering the whole mapped area each time. This mutable slice implements Write by advancing the pointer and adjusting the length.

If you want consecutive calls to your write function append data to the end, you will either have to keep the mutable slice around or as you suggest keep your own cursor/position/offset around and do m_mut.deref_mut()[self.pos..].write_all(data).unwrap(); followed by self.pos += data.len();.

[rockit-ba]

The call to m_mut.deref_mut() produces a mutable slice &mut [u8] covering the whole mapped area each time. This mutable slice implements Write by advancing the pointer and adjusting the length.

If you want consecutive calls to your write function append data to the end, you will either have to keep the mutable slice around or as you suggest keep your own cursor/position/offset around and do m_mut.deref_mut()[self.pos..].write_all(data).unwrap(); followed by self.pos += data.len();.
yes,i do that, like self.pos += data.len()，thanks very much