The clnt_sperrno routine returns a pointer to a string.

    Use this routine instead if:
    o  The server does not have a stderr file; many servers do not.
    o  You want to save the string.
    o  You do not want to use fprintf to print the message.
    o  The message format is different from the one that clnt_perrno
       supports.

    The address that clnt_sperrno returns is a pointer to the error
    message string for the error. Therefore, you do not have to copy
    the string to your own buffer in order to save the string.