Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!mit-eddie!mit-amt!mit-caf!vlcek
From: vlcek@mit-caf.MIT.EDU (Jim Vlcek)
Newsgroups: comp.lang.c
Subject: Point me in the right direction
Message-ID: <1841@mit-caf.MIT.EDU>
Date: 17 Feb 89 01:31:42 GMT
References: <23631@watmath.waterloo.edu>
Reply-To: vlcek@mit-caf.UUCP (Jim Vlcek)
Organization: Microsystems Technology Laboratories, MIT
Lines: 67

rbutterworth@watmath.waterloo.edu (Ray Butterworth) writes:

>Another handy style guideline to follow is trying to avoid writing
>empty [] declarations.  If the [] is empty, then you are talking
>about an array of unknown size and in the event that you really do
>want the array there is no way that the compiler will know how big
>it is.  If you don't know how big an array is, then perhaps you
>shouldn't be talking about arrays but about pointers.

No one caught this?  A compiler must be able to determine for itself
the size of one of the dimensions of an array (I believe the last
dimension in the case of a superlinear array, no?), if that array is
to be initialized at compile time, provided that unambiguous
initializers are provided.   In fact, for an array which is fully
initialized at compile time, an empty [] declaration is preferable:

double fund_consts[] = {
	3.14159265,
	2.7182818,
	6.02E23,
};

Should I want to add Euler's constant later, I merely splice it in at
the end -- I don't have to change the dimension parameter.  More
important, there's no danger of forgetting to change that parameter.

Also, I frequently work with static structures which are initialized at
compile time, and which I pass around via pointers.  Since

struct foo *bar = { /* Some aggregate initialization */ };

is illegal, I use

struct foo bar[] = { { /* Some aggregate initialization */ } };

which is legal and works so long as all of the elements of the
struct can be initialized (unfortunately, unions cannot).  This
construct achieves in one declaration what I need, although it does
somewhat abuse the concept of an array.  I'd be interested in hearing
comments on this technique.

>In particular never declare a function parameter as an array.
>e.g. use "char **argv;", not "char *argv[];".  Since the compiler
>will silently convert the second parameter declaration into the
>first for you, you might as well declare it that way in the first
>place and avoid confusing yourself and others.

I wouldn't say this.  I like the use of ``foo *bar[]'' to make it
clear that ``bar'' does indeed represent an array of pointers, through
which one might traverse.  Typically, however, I would use the first
form for the actual pointer used for the traversal:

some_fun(arglp) char *arglp[]; {
	char **next_arg = arglp;

	while (*next_arg++) {
	/* Party 'til you drop */
	}
}

Presuming, of course, that you want to preserve the head of the list
arglp, otherwise you could increment it directly.  Conceptually, the
above method is more clear in that next_arg is intended to refer to a
pointer to a single item, hence the use of char **.
-- 
Jim Vlcek
vlcek@caf.mit.edu
!{harvard,rutgers}!mit-eddie!mit-caf!vlcek