a compile error in kernel

1.Today , when I write a function in driver:
static void update_clients( )
{
...
}
compile prompt:
cc1: warnings being treated as errors
:26: error: function declaration isn't a prototype
resolved:
add void as follow:
static void update_clients(void )
This is C99 standard.
2. a error in c program
  the header file is written as follow:
  #ifndef __TEST_H
  ...
  #endif
  when compile, a error prompt:
  dereferencing pointer to incomplete type
  resolved:
     write correct header file.
  #ifndef __TEST_H
  #define __TEST_H
  #endif