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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Error message for a dangling pointer
Date: Mon, 06 Feb 2017 18:02:59 -0800
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ram@zedat.fu-berlin.de (Stefan Ram) writes:
>   For teaching purposes, I just wrote this program to show
>   dangling pointers:
>
> #include <stdio.h>
> int main( void )
> { int * p;
>   { int i = 27; p = &i; }
>   printf( "%d\n", *p ); }

(A side note: Your students might later have difficulties with more, um,
conventional C code layouts.)

>   I hope you all agree that »p« in the last line /is/
>   a dangling pointer.

Yes.

>   The error message and output is not what I expected,
>   but still interesting:
>
> main.c: In function 'main':
> main.c:6:3: warning: 'i' is used uninitialized in this function [-Wuninitialized]
>    printf( "%d\n", *p ); }
>    ^
> main.c:5:9: note: 'i' was declared here
>    { int i = 27; p = &i; }
>          ^
> 0
>
>   »i« /was/ initialized in the program,
>   so the error message is not accurate.
>
>   (I do not write »misleading«, since it is so
>   obviously wrong that it won't mislead anyone.)

I get that message with gcc 6.3.0, and with a gcc snapshot from
2017-01-12 that claims to be gcc 7.0.0, but not with gcc 6.2.0
(or with clang).

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"