lclint-interest message 24

Date: 14 Nov 94 16:38:00 EST
From: "JR (John Rogers)" <72634.2402@compuserve.com>
To: LCLint interest list 
Subject: Re: /*NOTREACHED*/ vs. /*@ -unreachable */ ?

Hi Dave!  I'm afraid I didn't make the effect of /*NOTREACHED*/
clear.  It doesn't turn off a check; it flags code which may affect
other checks.  Ian Darwin's book ("Checking C Programs with lint")
has a good 2-page explanation of this.  UNIX lint does not know about
exit() and other functions which never return.

Here's an updated version of your sample:

extern int something;

int f()
{
   if (something)
      exit(3);
   else
      return (2);
}
/* UNIX lint will say something like "found return(expr); and return;" */

Since f() is declared as returning int, UNIX lint will attempt to
detect whether or not all paths through the code actually return an
int value.  Since UNIX lint doesn't know that exit() never returns, it
thinks there is a path in f() might return without returning a value.
(That's the path where 'something' is true.)

int f()
{
   if (something) {
      exit(3);
      /* NOTREACHED */
   }
   else
      return (2);
}
/* UNIX lint should not complain about anything here */

The /*NOTREACHED*/ comment advises lint that the previous function call
(in this case, exit()) never returns.  Therefore, the rest of this code
path (presumably up to the next brace?) will not execute.  Therefore, it
need not complain that f() may return without returning a value.

PC-lint supports the /*NOTREACHED*/ comment for this reason.  PC-lint
knows about exit() not returning.  PC-lint also supports "function
mimicry", where just one "declaration" of a routine can be done.  For
instance:

In myheader.h:

   void MyDieRoutine( void );
   /*lint -function(exit,MyDieRoutine) */

Using this with PC-lint avoids having to flag every call to MyDieRoutine()
as /*NOTREACHED*/.

Anyway, to re-ask the question:  Does LCLint provide a way to handle
this situation at the point of call to a function which never returns?
How about when declaring a function which never returns?

Hope this helps...
--JR,