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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.lang.c
Subject: Re: Arcane C hacks?
Message-ID: <3374@umcp-cs.UUCP>
Date: Wed, 26-Feb-86 20:40:47 EST
Article-I.D.: umcp-cs.3374
Posted: Wed Feb 26 20:40:47 1986
Date-Received: Sat, 1-Mar-86 01:25:02 EST
References: <184@bu-cs.UUCP>, <592@bentley.UUCP> <1067@houxf.UUCP>
Organization: U of Maryland, Computer Science Dept., College Park, MD
Lines: 49

In article <1067@houxf.UUCP> jph@houxf.UUCP (Jack Harkins)

 . . . responds to the following from Barry Shein:

>>declare a table something like:   int (*funtable[MAXFNS])() ;
>>and just malloc the storage for the generated code.  ...  It should be
>>quite portable (code generator aside) and is legal C.
> 
>Well, some compilers will dislike the attempt to cast a (char *) into
>a (int (*)()) ; in fact I think some will call it an outright error

Jack Harkins says:

>This line of code DOES NOT cast a char * into an int. It is declaring
>that funtable is an array of MAXFNS elements, each of which is a pointer
>to a function that returns a int value.

You are both right.  It is obvious that the line Jack refers to is:

	int (*funtable[MAXFNS])();

while the code Barry refers to is:

	char *malloc();

	funtable[n] = (int (*)()) malloc(codesize);

(which does not appear in the quoted text, but is implied nonetheless.)

So when Barry says:

> it is _not_ portable to the 3b2,

he is correct: you cannot invoke the allocated function without
turning it into `code' first, for the hardware will not execute
`data'; and when Jack says:

>I have programs that use pointers to functions, some that run on 3B2/5's.
>The construct is totally(no flames, please) portable.

he is also correct: pointers to functions are portable.  It is this
specific usage---allocate data, fill with code, call data area as
function---that is not.

Hoping this will forestall further confusion,
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1415)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu