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Start an asynchronous write at the specified offset.

    typename ConstBufferSequence,
    typename WriteHandler>
DEDUCED async_write_some_at(
    uint64_t offset,
    const ConstBufferSequence & buffers,
    WriteHandler && handler);

This function is used to asynchronously write data to the random-access handle. The function call always returns immediately.



The offset at which the data will be written.


One or more data buffers to be written to the handle. Although the buffers object may be copied as necessary, ownership of the underlying memory blocks is retained by the caller, which must guarantee that they remain valid until the handler is called.


The handler to be called when the write operation completes. Copies will be made of the handler as required. The function signature of the handler must be:

void handler(
  const boost::system::error_code& error, // Result of operation.
  std::size_t bytes_transferred           // Number of bytes written.

Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. On immediate completion, invocation of the handler will be performed in a manner equivalent to using post.


The write operation may not transmit all of the data to the peer. Consider using the async_write_at function if you need to ensure that all data is written before the asynchronous operation completes.


To write a single data buffer use the buffer function as follows:

handle.async_write_some_at(42, boost::asio::buffer(data, size), handler);

See the buffer documentation for information on writing multiple buffers in one go, and how to use it with arrays, boost::array or std::vector.