Attempt to read a certain amount of data at the specified offset before returning.
template< typename SyncRandomAccessReadDevice, typename Allocator> std::size_t read_at( SyncRandomAccessReadDevice & d, uint64_t offset, basic_streambuf< Allocator > & b);
This function is used to read a certain number of bytes of data from a random access device at the specified offset. The call will block until one of the following conditions is true:
This operation is implemented in terms of zero or more calls to the device's read_some_at function.
The device from which the data is to be read. The type must support the SyncRandomAccessReadDevice concept.
The offset at which the data will be read.
object into which the data will be read.
The number of bytes transferred.
Thrown on failure.
This overload is equivalent to calling:
boost::asio::read_at( d, 42, b, boost::asio::transfer_all());