| 
                  a.read_some_at(b,
                  o,
                  mb,
                  ec); | 
                  size_t | 
                  pre: a.is_open(b).
 Reads one or more bytes of data from a handle
 bat offseto.
 The mutable buffer sequence
 mbspecifies memory where the data should be placed. The operation
                  shall always fill a buffer in the sequence completely before proceeding
                  to the next.
 If successful, returns the number of
                  bytes read. Otherwise returns
 0.
                  If the total size of all buffers in the sequencembis0,
                  the function shall return0immediately. | 
| 
                  a.async_read_some_at(b,
                  o,
                  mb,
                  rh); | 
                  void | 
                  pre: a.is_open(b).
 Initiates an asynchronous operation to read one or more
                  bytes of data from a handle
 bat offseto. The
                  operation is performed via theio_serviceobjecta.get_io_service()and behaves according to asynchronous
                  operation requirements.
 The mutable buffer
                  sequence
 mbspecifies
                  memory where the data should be placed. The operation shall always
                  fill a buffer in the sequence completely before proceeding to the
                  next.
 The implementation shall maintain one or more
                  copies of
 mbuntil
                  such time as the read operation no longer requires access to the
                  memory specified by the buffers in the sequence. The program must
                  ensure the memory is valid until:
 — the last copy of
 mbis destroyed,
                  or
 — the handler for the asynchronous operation is invoked,
 
 whichever comes first. If the total size of all buffers
                  in the sequence
 mbis0, the asynchronous
                  read operation shall complete immediately and pass0as the argument to the handler
                  that specifies the number of bytes read.
 If the operation
                  completes successfully, the
 ReadHandlerobjectrhis invoked
                  with the number of bytes transferred. Otherwise it is invoked with0. | 
| 
                  a.write_some_at(b,
                  o,
                  cb,
                  ec); | 
                  size_t | 
                  pre: a.is_open(b).
 Writes one or more bytes of data to a handle
 bat offseto.
 The constant buffer sequence
 cbspecifies memory where the data to be written is located. The operation
                  shall always write a buffer in the sequence completely before proceeding
                  to the next.
 If successful, returns the number of
                  bytes written. Otherwise returns
 0.
                  If the total size of all buffers in the sequencecbis0,
                  the function shall return0immediately. | 
| 
                  a.async_write_some_at(b,
                  o,
                  cb,
                  wh); | 
                  void | 
                  pre: a.is_open(b).
 Initiates an asynchronous operation to write one or more
                  bytes of data to a handle
 bat offseto. The
                  operation is performed via theio_serviceobjecta.get_io_service()and behaves according to asynchronous
                  operation requirements.
 The constant buffer
                  sequence
 cbspecifies
                  memory where the data to be written is located. The operation shall
                  always write a buffer in the sequence completely before proceeding
                  to the next.
 The implementation shall maintain one
                  or more copies of
 cbuntil such time as the write operation no longer requires access
                  to the memory specified by the buffers in the sequence. The program
                  must ensure the memory is valid until:
 — the last copy
                  of
 cbis destroyed,
                  or
 — the handler for the asynchronous operation is invoked,
 
 whichever comes first. If the total size of all buffers
                  in the sequence
 cbis0, the asynchronous
                  operation shall complete immediately and pass0as the argument to the handler that specifies the number of bytes
                  read.
 If the operation completes successfully, the
 WriteHandlerobjectwhis invoked with
                  the number of bytes transferred. Otherwise it is invoked with0. |