asio C++ library

basic_datagram_socket::async_send (1 of 2 overloads)

Start an asynchronous send on a connected socket.

    typename ConstBufferSequence,
    typename WriteToken = DEFAULT>
DEDUCED async_send(
    const ConstBufferSequence & buffers,
    WriteToken && token = DEFAULT);

This function is used to asynchronously send data on the datagram socket. It is an initiating function for an asynchronous operation, and always returns immediately.



One or more data buffers to be sent on the socket. 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 completion handler is called.


The completion token that will be used to produce a completion handler, which will be called when the send completes. Potential completion tokens include use_future, use_awaitable, yield_context, or a function object with the correct completion signature. The function signature of the completion handler must be:

void handler(
  const asio::error_code& error, // Result of operation.
  std::size_t bytes_transferred // Number of bytes sent.

Regardless of whether the asynchronous operation completes immediately or not, the completion handler will not be invoked from within this function. On immediate completion, invocation of the handler will be performed in a manner equivalent to using post.

Completion Signature
void(asio::error_code, std::size_t)

The async_send operation can only be used with a connected socket. Use the async_send_to function to send data on an unconnected datagram socket.


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

socket.async_send(asio::buffer(data, size), handler);

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

Per-Operation Cancellation

On POSIX or Windows operating systems, this asynchronous operation supports cancellation for the following cancellation_type values: