Attempt to read a certain amount of data at the specified offset before returning.

template<
    typename SyncRandomAccessReadDevice,
    typename MutableBufferSequence>
std::size_t read_at(
    SyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    const MutableBufferSequence & buffers);

template<
    typename SyncRandomAccessReadDevice,
    typename MutableBufferSequence,
    typename CompletionCondition>
std::size_t read_at(
    SyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    const MutableBufferSequence & buffers,
    CompletionCondition completion_condition);

template<
    typename SyncRandomAccessReadDevice,
    typename MutableBufferSequence,
    typename CompletionCondition>
std::size_t read_at(
    SyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    const MutableBufferSequence & buffers,
    CompletionCondition completion_condition,
    boost::system::error_code & ec);

template<
    typename SyncRandomAccessReadDevice,
    typename Allocator>
std::size_t read_at(
    SyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    basic_streambuf< Allocator > & b);

template<
    typename SyncRandomAccessReadDevice,
    typename Allocator,
    typename CompletionCondition>
std::size_t read_at(
    SyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    basic_streambuf< Allocator > & b,
    CompletionCondition completion_condition);

template<
    typename SyncRandomAccessReadDevice,
    typename Allocator,
    typename CompletionCondition>
std::size_t read_at(
    SyncRandomAccessReadDevice & d,
    boost::uint64_t offset,
    basic_streambuf< Allocator > & b,
    CompletionCondition completion_condition,
    boost::system::error_code & ec);