Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of Boost. Click here to view this page for the latest version.

write_at (2 of 8 overloads)

Write all of the supplied data at the specified offset before returning.

    typename SyncRandomAccessWriteDevice,
    typename ConstBufferSequence>
std::size_t write_at(
    SyncRandomAccessWriteDevice & d,
    uint64_t offset,
    const ConstBufferSequence & buffers,
    boost::system::error_code & ec);

This function is used to write a certain number of bytes of data to a random access device at a 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 write_some_at function.



The device to which the data is to be written. The type must support the SyncRandomAccessWriteDevice concept.


The offset at which the data will be written.


One or more buffers containing the data to be written. The sum of the buffer sizes indicates the maximum number of bytes to write to the device.


Set to indicate what error occurred, if any.

Return Value

The number of bytes transferred.


To write a single data buffer use the buffer function as follows:

boost::asio::write_at(d, 42,
    boost::asio::buffer(data, size), ec);

See the buffer documentation for information on writing multiple buffers in one go, and how to use it with arrays, boost::array or std::vector.


This overload is equivalent to calling:

    d, offset, buffers,
    boost::asio::transfer_all(), ec);