Start an asynchronous read at the specified offset.
template< typename MutableBufferSequence, typename ReadToken = DEFAULT> DEDUCED async_read_some_at( uint64_t offset, const MutableBufferSequence & buffers, ReadToken && token = DEFAULT);
This function is used to asynchronously read data from the random-access handle. It is an initiating function for an asynchronous operation, and always returns immediately.
The offset at which the data will be read.
One or more buffers into which the data will be read. 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 completion handler is called.
token that will be used to produce a completion handler, which
will be called when the read completes. Potential completion tokens
or a function object with the correct completion signature. The function
signature of the completion handler must be:
void handler( const asio::error_code& error, // Result of operation. std::size_t bytes_transferred // Number of bytes read. );
Regardless of whether the asynchronous operation completes immediately
or not, the completion 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
The read operation may not read all of the requested number of bytes. Consider
function if you need to ensure that the requested amount of data is read
before the asynchronous operation completes.
To read into a single data buffer use the
buffer function as follows:
handle.async_read_some_at(42, asio::buffer(data, size), handler);
documentation for information on reading into multiple buffers in one go,
and how to use it with arrays, boost::array or std::vector.
This asynchronous operation supports cancellation for the following