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From: Ian Collins <ian-news@hotmail.com>
Newsgroups: comp.lang.c
Subject: Re: Memory corruption on freeing a pointer to pointer
Date: Tue, 27 Aug 2013 09:42:53 +1200
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Xref: csiph.com comp.lang.c:35888

Ike Naar wrote:
> On 2013-08-26, Ian Collins <ian-news@hotmail.com> wrote:
>> Ike Naar wrote:
>>> On 2013-08-26, Ian Collins <ian-news@hotmail.com> wrote:
>>>> James Kuyper wrote:
>>>>> On 08/26/2013 02:40 AM, Ike Naar wrote:
>>>>>> On 2013-08-25, Keith Thompson <kst-u@mib.org> wrote:
>>>>>>> James Kuyper <jameskuyper@verizon.net> writes:
>>>>>>>> On 08/24/2013 03:05 PM, Sharwan Joram wrote:
>>>>>>> [...]
>>>>>>>>>              if ( NULL == parameters[parametercount]){
>>>>>>>
>>>>>>> This is what's known as a "Yoda conndition"
>>>>>>> <http://en.wikipedia.org/wiki/Yoda_Conditions>.  I know that a lot of
>>>>>>> programmers like them, and for somewhat valid reasons, but personally I
>>>>>>> find them jarring and unnecessary.  Personally, I'd write that as:
>>>>>>>
>>>>>>>        if (parameters[parametercount] == NULL) {
>>>>>>
>>>>>> Does it matter? The == operator is symmetric, (X==Y) == (Y==X).
>>>>>
>>>>> Yes, it matters - because it's intended to protect against the typo
>>>>> which replaces == with =, by ensuring that it would cause a constraint
>>>>> violation. The assignment operator is very definitely not symmetric.
>>>>
>>>> The best way to protect against that particular typo is decent unit tests.
>>>
>>> Do not overestimate the value of unit tests.
>>> Let's take, for example, a piece of code that multiplies two
>>> 32-bit numbers to obtain a 64-bit result.
>>
>> What has that got to do with this particular typo?
>
> Everything. If you know the typo in your progam, you
> don't need tests to find it, you just fix the typo.
> If you don't know there's a typo, the only way to be sure you
> find one is to test all possible cases.

But you will know as soon as you add the code and it fails its test.

-- 
Ian Collins