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#### posix::basic_stream_descriptor::async_read_some

Start an asynchronous read.

    template<
        typename MutableBufferSequence,
        typename ReadHandler>
    void async_read_some(
        const MutableBufferSequence & buffers,
        ReadHandler handler);

This function is used to asynchronously read data from the stream descriptor. The function call always returns immediately.

###### Parameters

buffers

  One or more buffers into which the data will be read. Although the buffers object may be copied as necessary, ownership of the underlying memory blocks is retained by the caller, which must guarantee that they remain valid until the handler is called.

handler

  The handler to be called when the read operation completes. Copies will be made of the handler as required. The function signature of the handler must be:

      void handler(
        const boost::system::error_code& error, // Result of operation.
        std::size_t bytes_transferred           // Number of bytes read.
      );

  Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using `boost::asio::io_service::post()`.

###### Remarks

The read operation may not read all of the requested number of bytes. Consider using the `async_read` function if you need to ensure that the requested amount of data is read before the asynchronous operation completes.

###### Example

To read into a single data buffer use the `buffer` function as follows:

    descriptor.async_read_some(boost::asio::buffer(data, size), handler);

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