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Path: utzoo!mnetor!seismo!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c,comp.bugs.4bsd
Subject: Re: Bad Pointer Declaration in 'scandir'
Message-ID: <5916@mimsy.UUCP>
Date: Sun, 22-Mar-87 22:07:07 EST
Article-I.D.: mimsy.5916
Posted: Sun Mar 22 22:07:07 1987
Date-Received: Tue, 24-Mar-87 01:45:13 EST
References: <2479@dalcs.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 49
Keywords: scandir, C, pointers, man
Xref: mnetor comp.lang.c:1312 comp.bugs.4bsd:244

In article <2479@dalcs.UUCP> dalegass@dalcs.UUCP (Dale Gass) writes:
>I believe there is a incorrect pointer declaration in the unix 'scandir'
>function (or manual page, at least) ... :
>
>struct direct *(*namelist[]);

Well, it is certainly misleading.

>According to my understanding, this should be interpreted as an array
>of pointers to pointers to the direct structure....  I believe [it should
>read] struct direct *(*namelist)[];

No: for there is no such thing.  A declaration for a pointer to an
array must specify the size of the array.  In fact, what both the
code and the manual *should* say is

	struct direct ***namelist;

That is, the function wants the address of a variable declared as
`struct direct **names;'.  An example would help:

	int i, nnames;
	struct direct **names;
	extern int alphasort();

	nnames = scandir("/tmp", &names, (int (*)()) NULL, alphasort);
	if (nnames < 0) {
		complain("cannot read /tmp");
		return;
	}
	for (i = 0; i < nnames; i++)
		/* do something with names[i]->d_name */

the code for the scandir function itself reads

	scandir(..., namelist, ...)
		...
		struct direct *(*namelist[]);
		...

The compiler, following the rules for conversion of parameter
declarations, alters this to `struct direct ***namelist', which
is of course correct.  (No wonder it works! :-) )

Also unfortunate, incidentally, is the lack of a function to free
the memory allocated by scandir().
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
UUCP:	seismo!mimsy!chris	ARPA/CSNet:	chris@mimsy.umd.edu