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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: guidelines for pointer check
Date: Thu, 29 Dec 2016 13:39:25 -0800
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Thiago Adams <thiago.adams@gmail.com> writes:
> Do you have some style guideline for pointer checking?
>
> This is a kind of poll:
>
>
>    //Style 1
>    if (pVariable) { /*...*/ }
>
>    //Style 2
>    if (pVariable != NULL)  { /*...*/ }
>
>    //Style 3
>    if (pVariable != 0) { /*...*/ }
>
> Do you dislike one of them?
> Do you use only one of them?
> Do you use more than one?
> Other?

I prefer `if (pVariable != NULL)`.

As Stefan Ram points out, NULL requires #including a standard header,
but in a program of any complexity one of the several standard headers
that define NULL will almost certainly already be #included -- and if
not, adding `#include <stddef.h.` is easy enough.

The other styles are of course perfectly valid, and those who prefer
them are not wrong.  I prefer NULL over 0 or the implicit comparison
of Style 1 because it's more explicit and isn't likely to introduce
any potential problems.  There might be some risk that pVariable
isn't really of pointer type, and that `if (pVariable != NULL)`
still compiles because NULL is defined as 0.  Similarly, I'd compare
a char value to '\0', a floating-point value to 0.0, and I wouldn't
compare boolean value (whether _Bool or not) to anything.

I'm not entirely consistent about prefering explicit code.  For example
I don't cast the result of malloc(), preferring the implicit conversion
of void* to the appropriate target type -- partly because the cast can
cause actual problems.

My preferences are almost certainly influenced by other languages I've
used.

-- 
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"