async_write_at (4 of 4 overloads)

Start an asynchronous operation to write a certain amount of data at the specified offset.

template<
    typename AsyncRandomAccessWriteDevice,
    typename Allocator,
    typename CompletionCondition,
    typename WriteHandler>
void async_write_at(
    AsyncRandomAccessWriteDevice & d,
    boost::uint64_t offset,
    basic_streambuf< Allocator > & b,
    CompletionCondition completion_condition,
    WriteHandler handler);

This function is used to asynchronously write a certain number of bytes of data to a random access device at a specified offset. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

All of the data in the supplied basic_streambuf has been written.
The completion_condition function object returns 0.

This operation is implemented in terms of zero or more calls to the device's async_write_some_at function.

Parameters

d

The device to which the data is to be written. The type must support the AsyncRandomAccessWriteDevice concept.

offset

The offset at which the data will be written.

b

A basic_streambuf object from which data will be written. Ownership of the streambuf is retained by the caller, which must guarantee that it remains valid until the handler is called.

completion_condition

The function object to be called to determine whether the write operation is complete. The signature of the function object must be:

std::size_t completion_condition(
  // Result of latest async_write_some_at operation.
  const boost::system::error_code& error,

  // Number of bytes transferred so far.
  std::size_t bytes_transferred
);

A return value of 0 indicates that the write operation is complete. A non-zero return value indicates the maximum number of bytes to be written on the next call to the device's async_write_some_at function.

handler

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(
  // Result of operation.
  const boost::system::error_code& error,

  // Number of bytes written from the buffers. If an error
  // occurred, this will be less than the sum of the buffer sizes.
  std::size_t bytes_transferred
);

Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using boost::asio::io_service::post().