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#### Random-Access HANDLEs

Boost.Asio provides Windows-specific classes that permit asynchronous read and write operations to be performed on HANDLEs that refer to regular files.

For example, to perform asynchronous operations on a file the following object may be created:

    HANDLE handle = ::CreateFile(...);
    windows::random_access_handle file(my_io_context, handle);

Data may be read from or written to the handle using one of the `read_some_at()`, `async_read_some_at()`, `write_some_at()` or `async_write_some_at()` member functions. However, like the equivalent functions (`read_some()`, etc.) on streams, these functions are only required to transfer one or more bytes in a single operation. Therefore free functions called read_at(), async_read_at(), write_at() and async_write_at() have been created to repeatedly call the corresponding `*_some_at()` function until all data has been transferred.

###### See Also

windows::random_access_handle.

###### Notes

Windows random-access `HANDLE`s are only available at compile time when targeting Windows and only when the I/O completion port backend is used (which is the default). A program may test for the macro `BOOST_ASIO_HAS_WINDOWS_RANDOM_ACCESS_HANDLE` to determine whether they are supported.