How to read data from the instrument using ni-visa in cpp

using the viRead() i am not able to fetch the output from my rigol oscilloscope .

First i am giving the data using viWrite() to the oscilloscope to print sine wave with some frequency and voltage .This works properly .

After this i am calling viRead  with SCPI command "WAVeform:data" to fetch data from the oscilloscope but getting some errors. 

Can please someone help me in this .(by providing the steps to how to fetch data from instrument or which api's of ni-visa to use for fetching the data).