[vbox-dev] [PATCH 2/8] Fix an implicit conversion from pointer to bool

[Michal Necasek]

 The question isn't whether a compiler can warn. The question is, why should it?

 What you quoted doesn't contradict what Frank said. There is a very well defined pointer to bool conversion. So what's the problem? Or in other words, what is the semantic difference between

    if (ptr)

 and

    if (ptr != NULL)

 (in whatever is the today's blessed flavor of C++)? It's not obvious to me.


     Regards,
       Michal

----- Original Message -----
From: jkim at FreeBSD.org
To: frank.mehnert at oracle.com, vbox-dev at virtualbox.org
Sent: Thursday, March 26, 2015 6:50:08 PM GMT +01:00 Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna
Subject: Re: [vbox-dev] [PATCH 2/8] Fix an implicit conversion from pointer to bool

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Hash: SHA256

On 03/26/2015 04:51, Frank Mehnert wrote:
> Hi,
> 
> On Friday 13 March 2015 16:56:56 Jung-uk Kim wrote:
>> This fix an implicit conversion from pointer to bool.
> 
> why is this patch necessary? An expression like
> 
> if (pointer) { }
> 
> is completely valid and no compiler should warn about it. It tests
> if the pointer has a value different from NULL.

Pointer is NOT bool.  Actually, the pointer is *implicitly* converted
to bool type here and compiler can warn about it.  Excerpt from C++11:

4.12 Boolean conversions

A prvalue of arithmetic, unscoped enumeration, pointer, or pointer to
member type can be converted to a prvalue of type bool. A zero value,
null pointer value, or null member pointer value is converted to
false; any other value is converted to true. A prvalue of type
std::nullptr_t can be converted to a prvalue of type bool; the
resulting value is false.

> Would
> 
> -         || (   (a_pVCpu) /*!= NULL*/ \ +         || (   a_pVCpu
> \
> 
> fix the compiler warning as well?

No, I don't think so.

Jung-uk Kim
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