quicsample server redirecting log to file

[zhanghenan-dev]

Please tell me how to redirect quicsample stdout to a file?

I execute quicsample normally, it has log print, I use printf function.As follows:
[root@localhost Debug]# ./quicsample -server -cert_file:cert_pem -key_file:priv_key
[AUTH SERVER]: 10:49:57 auth_main_init:829: auth init, cpu num:4
Press Enter to exit.

If I want to redirect stdout to a file, I try multiple method, but have no effect.
[root@localhost Debug]# ./quicsample -server -cert_file:cert_pem -key_file:priv_key > /root/msquic_server.log
[root@localhost ~]# ll msquic_server.log
-rwxrwxrwx 1 root root 0 May 18 10:58 msquic_server.log

I write a test file, it proved not my system problem.I don't know where is problem?