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From: dg@wrs.UUCP (David Goodenough)
Newsgroups: comp.lang.c
Subject: Re: Buffer referencing between functions.
Message-ID: <431@wrs.UUCP>
Date: Mon, 26-Oct-87 20:05:29 EST
Article-I.D.: wrs.431
Posted: Mon Oct 26 20:05:29 1987
Date-Received: Sat, 31-Oct-87 06:39:10 EST
References: <10756@sri-spam.istc.sri.com>
Reply-To: dg@wrs.UUCP (David Goodenough)
Organization: Wind River Systems, Emeryville, CA
Lines: 58
Keywords: *(auto_variables) in calling functions?

In article <10756@sri-spam.istc.sri.com> robert@sri-spam.istc.sri.com (Robert Allen) writes:
>    Below is a code fragment to illustrate my problem;
>
>    struct stack_vars {
>	char *frombuf;
>	int frombuf_index;	/* 0-2000 */
>	char *tobuf;
>	int tobuf_index;	/* 0-2000 */
>    };
>
>    void calling(inbuf,inbuf_index)
>    char inbuf[];
>    int inbuf_index;
>    {
>	struct stack_vars data;
>	char dbuf[2000];
>
>	data.frombuf = inbuf;
>	data.frombuf_index = inbuf_index;
>	data.tobuf = dbuf;
>	data.tobuf_index = 0;
>	called(&data);
>    }
>
>    void called(sv)
>    struct stack_vars *sv;
>    {
>	bcopy(sv->frombuf,sv->tobuf,sv->frombuf_index);
>	sv->tobuf_index = sv->frombuf_index;
>    }

Referencing dbuf via the pointer data.tobuf in the above section is legal,
fair game, and I do similar sorts of things all the time. The main danger
when passing pointers to locals around on the stack is NOT TO DO THIS:

	char *stug()
	 {
	    char blurf[100];

	    /* do something interesting */

	    return(blurf);
	 }

I.E. Don't return a pointer to a local variable, because by the time you use
it it is no longer valid, at best it will still be there, at worst another
procedure call will have overwritten it.
--
		dg@wrs.UUCP - David Goodenough

		..... !rtech!--\
				>--!wrs!dg
		  ..... !sun!--/

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