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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: double free
Date: Tue, 05 Jul 2016 08:43:14 -0700
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Richard Heathfield <rjh@cpax.org.uk> writes:
> On 05/07/16 13:16, Richard Bos wrote:
> <snip>
>
>> Ditch this book. It is misleading you, and the author is incompetent.
>
> Possible. Also possible: the author has been misquoted and/or 
> misinterpreted. (I have no evidence either way. I just know how very, 
> very possible it is.)

The book in question is "Understanding and Using C Pointers" by Richard
Reese, published by O'Reilly.  I have a copy.

http://shop.oreilly.com/product/0636920028000.do

The quoted excerpts are accurate, with one small wording change.
G G referred to a "runtime error".  The actual wording in the book's
discussion of a "double free" is:

    The term *double free* refers to an attempt to free a block of
    memory twice. A simple example follows:

        int *pi = (int*) malloc(sizeof(int));
        *pi = 5;
        free(pi);
        ...
        free(pi);

    The execution of the second free function will result in a runtime
    exception.

The phrase "runtime error", as Eric Sosman points out, could be
consistent with undefined behavior, which might have no visible
effects.  The phrase "runtime exception", I think, clearly implies
some visible result.  (I don't assume it refers to C++ exceptions.)

FWIW, when I run the above code on my own system, there is an
explicit runtime error:

    *** Error in `./c': double free or corruption (fasttop): 0x0000000008829010 ***
    Aborted

On another system (Solaris 9), there is no visible indication of
an error.  Both are of course consistent with the undefined behavior
of this construct.

-- 
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"