How to view LOG from nRF52840 USB CDC example

Question

Hi, I am working on the project through the USB CDC example. 
 I know how to view log using RTT Viewer through J-Link and UART-LOG using UART. 
 But how can I see LOG with only CDC-USB connected? 
 I am using Putty to connect to the COM port that came with the CDC-USB, and the CDC does not work. If I am running CDC, I can not see the LOG. 
 I wonder if there is a way to view LOG with only USB-CDC connected except the above two methods.

Stian Røed Hafskjold · Accepted Answer

Unfortunately, there's no built-in functionality to redirect the logging calls to the USB peripheral. However, you can define your own backed for logging. If you look at nrf_log_backend_uart.c you can see how the backend is implemented, so you can use this as a starting point and rewrite it for the USB peripheral. 
 Or, you can start out with the USB CDC example in the sdk and use app_usbd_cdc_acm_write() to print out your log messages.