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Path: utzoo!utgpu!water!watmath!clyde!rutgers!dayton!viper!john
From: john@viper.UUCP
Newsgroups: comp.sys.ibm.pc,comp.lang.c
Subject: Re: Assigning to Pointers
Message-ID: <967@viper.UUCP>
Date: Tue, 12-May-87 15:09:57 EDT
Article-I.D.: viper.967
Posted: Tue May 12 15:09:57 1987
Date-Received: Fri, 15-May-87 04:48:20 EDT
References: <3537@vrdxhq.UUCP> <857@killer.UUCP>
Reply-To: john@viper.UUCP (John Stanley)
Organization: DynaSoft Systems
Lines: 77
Xref: utgpu comp.sys.ibm.pc:3495 comp.lang.c:2061

In article <857@killer.UUCP> jfh@killer.UUCP (John Haugh) writes:
 >In article <3537@vrdxhq.UUCP>, tom@vrdxhq.UUCP (Tom Welsh) writes:
 >> 
 >> I want to do the following :
 >> 
 >> 
 >> int *aa[];
 >This is not a pointer to an array.  This is an array of pointers.  So,
 >the assignment
 >> aa = 0x50000;
 >doesn't make much sense.  If you want a pointer to an array, you could
 >try
 >int	**aa;

Correct so far....

 >  If you REALLY want a pointer to an array, how about
 >int	*(aa[]);

How about because it's not a pointer to an array?

A pointer to an array of int would be:
	int (*aa)[];

What you gave ( int *(aa[]); ) is identical to ( int *aa[]; ) which is
actualy an array of pointers to ints...  The [] binds to aa with a higher
precedence than the *.

 >  My weakness is pointers to functions -

  So I see...  If it's any consolation, it's taken me a few years to
get to the point where I get them right most of the time.  I know
many programmers who're excelent programmers, but even after 5-10
years they still get function pointers wrong now and then...

  I suspect the problem Tom Welsh is having is from the incorrect
(but often used) habit some programmers have of defining a pointer
to an array of pointers in-the-parameter-list as:

	foo(aa)
	int *aa[];
	{
	....

  Now, because C "knows" that you can't pass an array, it translates
the *aa[] into **aa but doesn't tell the programmer about it.  Any
reference to aa[x] is (per standard C) corectly converted to *(aa+x)
which will work for an array or a pointer.  Unfortunately for Tom,
this doesn't work anywhere except as part of the parameter list.  If
you have the sample I gave above, then aa = (int**)0x50000; will
work with no problem, but it won't work at-all if you try it with a 
non-function-argument variable since the identifier aa will then refer 
to a non-moveable array.

  Your best bet is to correctly define it as int **aa; in the first
place and avoid using the [] for for a pointer in parameter lists to
avoid future confusion...


 >I won't even bother with POINTER to FUNCTION returning POINTER to FUNCTION
 >returning an integer. 

Just for the hell of it...  B-) ...:

	int (*((*foo)()))();


 >Disclaimer:
 >	I don't have the slightest idea what I am talking about.  I can't
 >	handle these problems either.

  Oh...  (falseto voice)  "Nevermind..."  :)

--- 
John Stanley (john@viper.UUCP)
Software Consultant - DynaSoft Systems
UUCP: ...{amdahl,ihnp4,rutgers}!{meccts,dayton}!viper!john