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Groups > comp.lang.c > #103395
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|---|---|
| From | Manfred <noname@invalid.add> |
| Newsgroups | comp.lang.c |
| Subject | Re: Error message for a dangling pointer |
| Date | Tue, 7 Feb 2017 18:42:15 +0100 |
| Organization | Aioe.org NNTP Server |
| Lines | 32 |
| Message-ID | <o7d0tl$iis$2@gioia.aioe.org> (permalink) |
| References | <dangling-pointers-20170207022252@ram.dialup.fu-berlin.de> <1btw8654l6.fsf@pfeifferfamily.net> |
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On 2/7/2017 5:49 PM, Joe Pfeiffer wrote: > ram@zedat.fu-berlin.de (Stefan Ram) writes: > >> For teaching purposes, I just wrote this program to show >> dangling pointers: >> <snip> > I get the message in > gcc (Debian 6.2.1-5) 6.2.1 20161124 > if I turn optimization -O1 on. Also, without optimization the output is > 27 > while with optimization it is > 0 > > I think we can see the code analysis that's leading to the conclusion > that i is being used uninitialized (*p is being replaced by i, which is > not even defined in the scope in which it is being used, let alone > initialized). > > Even without the incorrect warning, I have to wonder how useful an > example of a dangling pointer this would be for students. Since I'd be > *really* surprised to see an actual implementation really allocate a > stack frame for the inner braces, the lecture would go sort of "see? A > dangling pointer. And it does exactly the same thing it would have done > if the pointer weren't dangling. That's why we should avoid dangling > pointers" (and of course that's exactly what happens with gcc, without > optimization). Coax malloc() into reallocating space you can overwrite > the contents or something.... > Maybe a dangling pointer assigned (and lost) in a function call could be more explicit than with inner braces? Eventually overwriting the stack frame with a second function call?
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Re: Error message for a dangling pointer Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2017-02-07 09:49 -0700
Re: Error message for a dangling pointer Manfred <noname@invalid.add> - 2017-02-07 18:42 +0100
Re: Error message for a dangling pointer Manfred <noname@invalid.add> - 2017-02-07 19:09 +0100
Re: Error message for a dangling pointer Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2017-02-07 21:20 -0700
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