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read_at (6 of 8 overloads)

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

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

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.


The basic_streambuf object into which the data will be read.


Set to indicate what error occurred, if any.

Return Value

The number of bytes transferred.


This overload is equivalent to calling:

    d, 42, b,
    boost::asio::transfer_all(), ec);