lclint-interest message 92

From evans@cs.virginia.edu Thu Jul 18 22:11:36 1996
Date: Thu, 18 Jul 96 22:10:30 -0400
From: evans@cs.virginia.edu (David Evans)
To: lclint-interest@larch.lcs.mit.edu
Cc: oh@cis.ohio-state.edu
In-Reply-To: Seung-Hong Oh's message of Thu, 18 Jul 1996 21:34:26 -0400 (EDT) 
Subject: Initialising arrays in loops


There's no specific way to do this, but you could define a macro to have
the same effect:

extern void MARK_DEFINED (/*@out@*/ void *);

/*@+allmacros@*/
/*@-macroparams@*/
# define MARK_DEFINED(x)
/*@=macroparams@*/
/*@=allmacros@*/

int f (void)
{
  struct { int x; } *st;
  
  st = malloc (sizeof (*st));
  assert (st != NULL);

  MARK_DEFINED (st); /* convinces lclint that st is completely defined */
  return st->x; /* no use before definition error is reported */
  /* (of course, there is still a memory leak reported) */
}

This is probably worth explaining more carefully:

The parameter to MARK_DEFINED is annotated with /*@out@*/.  This means
it need not be defined before the call, but is completely defined after
the call returns.  (This version of MARK_DEFINED only works for
pointers;  if we need to make it work for other types as well, we could
use alternate types, e.g., /*@alt int@*/, in the declaration.)

The definition of MARK_DEFINED is simply empty, so this will have no
effect on the compiled code.  Its surrounded by two lclint comments:

	/*@+allmacros@*/ means don't expand macro definitions
		(hence, MARK_DEFINED will not be replaced with nothing
		 where it is used)
        /*@-macroparams@*/ prevents lclint from complaining that the
		macro parameter x is not used in the body of the macro

The two /*@=...@*/ lines reset these flags to their previous values.

--- Dave