How to add a name to namespace

Dear all:
  As i kown, i can use the "clone" to create a process and a namespace, but the namespace created in this way has no name. For example, i create a network namespace with the parameter: CLONE_NEWNS, but in the command "ip netns list", there is no namespace list because the namespace created has no name. But i can use the command "ip netns add xxx" to create a namespace with the name "xxx".
  I wonder how to create a namespace with name using system call "clone".
  Thankyou verymuch for anyone's reply.

Best regards,
Vinllen