void *nng_aio_get_output(nng_aio *aio, unsigned int index);
nng_aio_get_output() function returns the output result at index
resulting from the asynchronous operation associated with aio.
The type and semantics of output parameters are determined by specific operations.
If the index does not correspond to a defined output for the operation,
or the operation did not succeed, then the return value will be
|It is an error to call this function while the aio is currently in use by an active asynchronous operation, or if no operation has been performed using the aio yet.
The indexth result of the operation, or