|
Start an asynchronous read at the specified offset.
template<
typename MutableBufferSequence,
typename ReadHandler = DEFAULT>
DEDUCED async_read_some_at(
uint64_t offset,
const MutableBufferSequence & buffers,
ReadHandler && handler = DEFAULT);
This function is used to asynchronously read data from the random-access handle. The function call 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 handler is called.
The handler to be called when the read operation completes. Copies will be made of the handler as required. The function signature of the 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 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 read operation may not read all of the requested number of bytes. Consider
using the async_read_at
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);
See the buffer
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 cancellation_type
values:
cancellation_type::terminal
cancellation_type::partial
cancellation_type::total