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which of these 3 casts would you prefer?

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  which of these 3 casts would you prefer? "A" <a@a.a> - 2011-08-25 23:58 +0200
    Re: which of these 3 casts would you prefer? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2011-08-25 16:19 -0700
    Re: which of these 3 casts would you prefer? Robert Wessel <robertwessel2@yahoo.com> - 2011-08-25 18:59 -0500
    Re: which of these 3 casts would you prefer? "Alf P. Steinbach" <alf.p.steinbach:usenet@gmail.com> - 2011-08-26 08:02 +0200
    Re: which of these 3 casts would you prefer? "Duga Chernobyl" <duga_c3@gmx.com> - 2011-08-26 10:05 +0200
      Re: which of these 3 casts would you prefer? "A" <a@a.a> - 2011-08-26 14:40 +0200
        Re: which of these 3 casts would you prefer? Leigh Johnston <leigh@i42.co.uk> - 2011-08-26 13:59 +0100
        Re: which of these 3 casts would you prefer? "Duga Chernobyl" <duga_c3@gmx.com> - 2011-08-26 15:19 +0200
          Re: which of these 3 casts would you prefer? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-26 21:27 +0000
            Re: which of these 3 casts would you prefer? "Alf P. Steinbach" <alf.p.steinbach:usenet@gmail.com> - 2011-08-27 01:28 +0200
            Re: which of these 3 casts would you prefer? "Duga Chernobyl" <duga_c3@gmx.com> - 2011-08-27 10:23 +0200
              Re: which of these 3 casts would you prefer? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-27 12:10 +0000
            Re: which of these 3 casts would you prefer? RaZiel <raziel_206_@hotmail.com> - 2011-08-27 21:55 +0200
            Re: which of these 3 casts would you prefer? Miles Bader <miles@gnu.org> - 2011-09-01 08:03 +0900
              Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-08-31 23:11 -0700
              Re: which of these 3 casts would you prefer? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-09-01 19:34 +0000
                Re: which of these 3 casts would you prefer? Joshua Maurice <joshuamaurice@gmail.com> - 2011-09-01 15:37 -0700
                  Re: which of these 3 casts would you prefer? gwowen <gwowen@gmail.com> - 2011-09-02 00:30 -0700
                    Re: which of these 3 casts would you prefer? Miles Bader <miles@gnu.org> - 2011-09-03 18:26 +0900
        Re: which of these 3 casts would you prefer? Edek <edek.pienkowski@gmail.com> - 2011-08-26 15:29 +0200
        Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-08-27 09:35 -0700
          Re: which of these 3 casts would you prefer? Juha Nieminen <nospam@thanks.invalid> - 2011-08-27 18:38 +0000
            Re: which of these 3 casts would you prefer? Noah Roberts <roberts.noah@gmail.com> - 2011-08-27 12:32 -0700
              Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-08-27 14:51 -0700
                Re: which of these 3 casts would you prefer? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-29 14:10 +0000
                  Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-08-30 07:23 -0700
              Re: which of these 3 casts would you prefer? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-29 11:32 +0000
            Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-08-27 14:37 -0700
              Re: which of these 3 casts would you prefer? Ian Collins <ian-news@hotmail.com> - 2011-08-28 10:06 +1200
                Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-08-27 15:27 -0700
                  Re: which of these 3 casts would you prefer? Ian Collins <ian-news@hotmail.com> - 2011-08-28 10:47 +1200
                  Re: which of these 3 casts would you prefer? Noah Roberts <roberts.noah@gmail.com> - 2011-08-27 15:42 -0700
                  Re: which of these 3 casts would you prefer? Nobody <nobody@nowhere.com> - 2011-08-28 04:15 +0100
              Re: which of these 3 casts would you prefer? Noah Roberts <roberts.noah@gmail.com> - 2011-08-27 15:52 -0700
                Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-08-28 01:54 -0700
                  Re: which of these 3 casts would you prefer? Keith H Duggar <duggar@alum.mit.edu> - 2011-09-04 19:16 -0700
              Re: which of these 3 casts would you prefer? Juha Nieminen <nospam@thanks.invalid> - 2011-08-29 18:16 +0000
                Re: which of these 3 casts would you prefer? Noah Roberts <roberts.noah@gmail.com> - 2011-08-29 16:35 -0700
                  Re: which of these 3 casts would you prefer? Nobody <nobody@nowhere.com> - 2011-08-30 04:13 +0100
                  Re: which of these 3 casts would you prefer? Juha Nieminen <nospam@thanks.invalid> - 2011-08-30 06:03 +0000
                Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-08-30 07:12 -0700
                  Re: which of these 3 casts would you prefer? Juha Nieminen <nospam@thanks.invalid> - 2011-08-31 06:16 +0000
                    Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-09-01 03:05 -0700
                      Re: which of these 3 casts would you prefer? Juha Nieminen <nospam@thanks.invalid> - 2011-09-01 07:00 +0000
                        Re: which of these 3 casts would you prefer? BGB <cr88192@hotmail.com> - 2011-08-31 13:21 -0700
            Re: which of these 3 casts would you prefer? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-28 19:30 +0000
        Re: which of these 3 casts would you prefer? Noah Roberts <roberts.noah@gmail.com> - 2011-08-27 12:19 -0700
          Re: which of these 3 casts would you prefer? Dombo <dombo@disposable.invalid> - 2011-08-28 12:08 +0200
          Re: which of these 3 casts would you prefer? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-28 19:44 +0000
            Re: which of these 3 casts would you prefer? Noah Roberts <roberts.noah@gmail.com> - 2011-08-28 13:41 -0700
      Re: which of these 3 casts would you prefer? Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2011-08-26 07:30 -0700

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#9326 — which of these 3 casts would you prefer?

int Callback(void *pThis)
{
TMyClass *pMC = (TMyClass*)pThis;                    // C style

TMyClass *pMC = static_cast<TMyClass*>(pThis);       // C++ style but the
                                                     // same as above

TMyClass *pMC = reinterpret_cast<TMyClass*>(pThis);  // Doesn't check if
                                                     // input type was
                                                     // pointer, possibly
                                                     // dangerous
}

these 3 do essentially the same. is there any preferred one for void* cast
like this and why? any difference in speed?

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#9327

On 8/25/2011 2:58 PM, A wrote:
> int Callback(void *pThis)
> {
> TMyClass *pMC = (TMyClass*)pThis;                    // C style
>
> TMyClass *pMC = static_cast<TMyClass*>(pThis);       // C++ style but the
>                                                       // same as above
>
> TMyClass *pMC = reinterpret_cast<TMyClass*>(pThis);  // Doesn't check if
>                                                       // input type was
>                                                       // pointer, possibly
>                                                       // dangerous
> }
>
> these 3 do essentially the same. is there any preferred one for void* cast
> like this and why? any difference in speed?

Casts from `void *` are handled in C++ by `static_cast`. So, that would 
be the one to use in this case. There's no reason to involve a less 
restrictive cast (`reinterpret_cast`) when a more restrictive does the 
job. That's basically the rule I'd follow: in any situation prefer to 
use the most restrictive cast that does the job.

-- 
Best regards,
Andrey Tarasevich

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#9328

On Thu, 25 Aug 2011 23:58:56 +0200, "A" <a@a.a> wrote:

>int Callback(void *pThis)
>{
>TMyClass *pMC = (TMyClass*)pThis;                    // C style
>
>TMyClass *pMC = static_cast<TMyClass*>(pThis);       // C++ style but the
>                                                     // same as above
>
>TMyClass *pMC = reinterpret_cast<TMyClass*>(pThis);  // Doesn't check if
>                                                     // input type was
>                                                     // pointer, possibly
>                                                     // dangerous
>}
>
>these 3 do essentially the same. is there any preferred one for void* cast
>like this and why? any difference in speed?


Obviously the first rule is to avoid casts where possible.   I avoid
the C-style casts, simply because they don't stand out well enough,
plus they can turn into anything from a const to a reinterpret cast.
And then I try to use the "weakest" cast that does the job - even if
the "stronger" cast does the exact same thing, it has a greater
possibility of hiding an error, in either current or future code. IOW,
const_cast is preferable to static_cast, is preferable to
reinterpert_cast (which should get pretty rare usage).  dynamic_cast
is a bit special, since it's not actually unsafe (although you do have
to handle the exception if it fails), and is not available in a
significant number of projects (the extra overhead dynamic_cast and
RTTI requires can usually be disabled with a compiler option).

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#9329

On 25.08.2011 23:58, A wrote:
> int Callback(void *pThis)
> {
> TMyClass *pMC = (TMyClass*)pThis;                    // C style
>
> TMyClass *pMC = static_cast<TMyClass*>(pThis);       // C++ style but the
>                                                       // same as above
>
> TMyClass *pMC = reinterpret_cast<TMyClass*>(pThis);  // Doesn't check if
>                                                       // input type was
>                                                       // pointer, possibly
>                                                       // dangerous
> }
>
> these 3 do essentially the same. is there any preferred one for void* cast
> like this and why? any difference in speed?

Aim for clarity.

Cheers & hth.,

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#9331

Dnia 25-08-2011 o 23:58:56 A <a@a.a> napisał(a):

> int Callback(void *pThis)
> {
> TMyClass *pMC = (TMyClass*)pThis;                    // C style
>
> TMyClass *pMC = static_cast<TMyClass*>(pThis);       // C++ style but the
>                                                      // same as above
>
> TMyClass *pMC = reinterpret_cast<TMyClass*>(pThis);  // Doesn't check if
>                                                      // input type was
>                                                      // pointer, possibly
>                                                      // dangerous
> }
>
> these 3 do essentially the same. is there any preferred one for void*  
> cast
> like this and why? any difference in speed?
>
>
>
>

IMHO there is no place for preferences.

The first is used in c and should be used only in C.
The second is from C++ and should be used mostly (compiler check if  
conversion is usable)
The third is a equivalent of the c solution. Compiler checks nothing.

In c++ should be used only c++ conversion, because mostly compiler (not in  
reinterpret conv.) does some checks of common sense of this conversion.
And c++ conversion are long and easy to find. The creator of c++ some gave  
arguments: the place of most errors is conversion ;-)

dynamic_cast is used for child class pointers conversion.
 

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#9333

I do not understand though reluctance to use C style casts.

They can cast to reinterpret_cast but they also try out the weaker cast 
before. It is just automatic way to do what you would do manually - first 
try const_cast, then static_cast and finally reinterpret_cast... yes, it can 
use reinterpret_cast but you would have to use it anyway in a particular 
case where you really need it.

So what's wrong with little automation, providing that you know what you are 
doing with casts? 

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#9334

On 26/08/2011 13:40, A wrote:
> I do not understand though reluctance to use C style casts.
>
> They can cast to reinterpret_cast but they also try out the weaker cast
> before. It is just automatic way to do what you would do manually - first
> try const_cast, then static_cast and finally reinterpret_cast... yes, it can
> use reinterpret_cast but you would have to use it anyway in a particular
> case where you really need it.
>
> So what's wrong with little automation, providing that you know what you are
> doing with casts?

Using C style casts is borderline obfuscation as you are not making it 
clear as to what you are doing; i.e. using an explicit C++ style cast is 
a form of self documenting code.

There is a potential for bug creation if you let a const_cast or 
reinterpret_cast through by mistake when using a C style cast.

Bottom line: prefer C++ style casts.

/Leigh

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#9335

Dnia 26-08-2011 o 14:40:27 A <a@a.a> napisał(a):

> I do not understand though reluctance to use C style casts.
>
> They can cast to reinterpret_cast but they also try out the weaker cast
> before. It is just automatic way to do what you would do manually - first
> try const_cast, then static_cast and finally reinterpret_cast... yes, it  
> can
> use reinterpret_cast but you would have to use it anyway in a particular
> case where you really need it.
>
> So what's wrong with little automation, providing that you know what you  
> are
> doing with casts?
>
>

Sometimes you are tired and you don't want to check, if something is good  
or bad. For me compiler is the best friend (in programming ;-)) and always  
set this settings:

Try search all convertions with c++ style and all with c style. What, do  
you think, is easier to find all of them?

-Wall -Wextra -pedantic -g -pg

It is not little automation, but great help ;-)

if you make a mistake f.e

if (a = 1) gcc will you ask, if really means it. If you are programmer,  
the common sense makes you to be open for all suggestions of compiler.
Many people thinks, that computer is evil, but computer makes exactly what  
we said (but not very often what we want ;-))

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#9352

On Fri, 2011-08-26, Duga Chernobyl wrote:
> Dnia 26-08-2011 o 14:40:27 A <a@a.a> napisa??(a):
>
>> I do not understand though reluctance to use C style casts.
>>
>> They can cast to reinterpret_cast but they also try out the weaker cast
>> before. It is just automatic way to do what you would do manually - first
>> try const_cast, then static_cast and finally reinterpret_cast... yes, it  
>> can
>> use reinterpret_cast but you would have to use it anyway in a particular
>> case where you really need it.
>>
>> So what's wrong with little automation, providing that you know what you  
>> are
>> doing with casts?

> Sometimes you are tired and you don't want to check, if something is good  
> or bad. For me compiler is the best friend (in programming ;-))

Yes, in C++ programming anyway.

> and always  
> set this settings:
>
> Try search all convertions with c++ style and all with c style. What, do  
> you think, is easier to find all of them?
>
> -Wall -Wextra -pedantic -g -pg

I'm surprised you're listing g++ warning options, but omit the topical
one: "-Wold-style-cast".  I use it for all my code.

/Jorgen

-- 
  // Jorgen Grahn <grahn@  Oo  o.   .     .
\X/     snipabacken.se>   O  o   .

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#9354

On 26.08.2011 23:27, Jorgen Grahn wrote:
>
> I'm surprised you're listing g++ warning options, but omit the topical
> one: "-Wold-style-cast".  I use it for all my code.

Thanks for that item.

Cheers,

- Alf

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#9359

Dnia 26-08-2011 o 23:27:03 Jorgen Grahn <grahn+nntp@snipabacken.se>  
napisał(a):

> On Fri, 2011-08-26, Duga Chernobyl wrote:
>> Dnia 26-08-2011 o 14:40:27 A <a@a.a> napisa??(a):
>>
>>> I do not understand though reluctance to use C style casts.
>>>
>>> They can cast to reinterpret_cast but they also try out the weaker cast
>>> before. It is just automatic way to do what you would do manually -  
>>> first
>>> try const_cast, then static_cast and finally reinterpret_cast... yes,  
>>> it
>>> can
>>> use reinterpret_cast but you would have to use it anyway in a  
>>> particular
>>> case where you really need it.
>>>
>>> So what's wrong with little automation, providing that you know what  
>>> you
>>> are
>>> doing with casts?
>
>> Sometimes you are tired and you don't want to check, if something is  
>> good
>> or bad. For me compiler is the best friend (in programming ;-))
>
> Yes, in C++ programming anyway.
>
>> and always
>> set this settings:
>>
>> Try search all convertions with c++ style and all with c style. What, do
>> you think, is easier to find all of them?
>>
>> -Wall -Wextra -pedantic -g -pg
>
> I'm surprised you're listing g++ warning options, but omit the topical
> one: "-Wold-style-cast".  I use it for all my code.
>
> /Jorgen
>

Thanks ;-)

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#9360

On Sat, 2011-08-27, Duga Chernobyl wrote:
> Dnia 26-08-2011 o 23:27:03 Jorgen Grahn <grahn+nntp@snipabacken.se>  
> napisa??(a):

>> I'm surprised you're listing g++ warning options, but omit the topical
>> one: "-Wold-style-cast".  I use it for all my code.

> Thanks ;-)

You're welcome :-) It took me a few years to discover that flag --
I think programmers in general read their manuals to rarely.

/Jorgen

-- 
  // Jorgen Grahn <grahn@  Oo  o.   .     .
\X/     snipabacken.se>   O  o   .

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#9367

On 26.08.2011 23:27, Jorgen Grahn wrote:
> On Fri, 2011-08-26, Duga Chernobyl wrote:
>> Dnia 26-08-2011 o 14:40:27 A<a@a.a>  napisa??(a):
>>
>>> I do not understand though reluctance to use C style casts.
>>>
>>> They can cast to reinterpret_cast but they also try out the weaker cast
>>> before. It is just automatic way to do what you would do manually - first
>>> try const_cast, then static_cast and finally reinterpret_cast... yes, it
>>> can
>>> use reinterpret_cast but you would have to use it anyway in a particular
>>> case where you really need it.
>>>
>>> So what's wrong with little automation, providing that you know what you
>>> are
>>> doing with casts?
>
>> Sometimes you are tired and you don't want to check, if something is good
>> or bad. For me compiler is the best friend (in programming ;-))
>
> Yes, in C++ programming anyway.
>
>> and always
>> set this settings:
>>
>> Try search all convertions with c++ style and all with c style. What, do
>> you think, is easier to find all of them?
>>
>> -Wall -Wextra -pedantic -g -pg
>
> I'm surprised you're listing g++ warning options, but omit the topical
> one: "-Wold-style-cast".  I use it for all my code.


For those who aren't using GCC, here is an alternative (Perl script):
http://www.abisource.com/mailinglists/abiword-dev/2003/May/0198.html

>
> /Jorgen
>

- RaZ

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#9579

Jorgen Grahn <grahn+nntp@snipabacken.se> writes:
> I'm surprised you're listing g++ warning options, but omit the topical
> one: "-Wold-style-cast".  I use it for all my code.

The problem with -Wold-style-cast, in my experience, is that
system/library headers are often chock-full of C-style casts,
resulting in huge quantities of warnings over which one has no
control...

-Miles

-- 
Rational, adj. Devoid of all delusions save those of observation, experience
and reflection.

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#9617

On 8/31/2011 4:03 PM, Miles Bader wrote:
> Jorgen Grahn<grahn+nntp@snipabacken.se>  writes:
>> I'm surprised you're listing g++ warning options, but omit the topical
>> one: "-Wold-style-cast".  I use it for all my code.
>
> The problem with -Wold-style-cast, in my experience, is that
> system/library headers are often chock-full of C-style casts,
> resulting in huge quantities of warnings over which one has no
> control...
>


well, as well as any code which is designed to work if compiled as 
either C or C++ (potentially including static-inline functions in 
headers, ...).

any such code would likely necessarily reflect the common subset of C 
and C++, which would mean C-style casts.

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#9619

On Wed, 2011-08-31, Miles Bader wrote:
> Jorgen Grahn <grahn+nntp@snipabacken.se> writes:
>> I'm surprised you're listing g++ warning options, but omit the topical
>> one: "-Wold-style-cast".  I use it for all my code.
>
> The problem with -Wold-style-cast, in my experience, is that
> system/library headers are often chock-full of C-style casts,
> resulting in huge quantities of warnings over which one has no
> control...

Haven't seen that happen yet. Either the warning is suppressed when
generated by a system header, or the ones I use (on Linux) happen to
be clean.

If I end up in that situation, of course I'll have to disable the
warnings for the affected translation units.

/Jorgen

-- 
  // Jorgen Grahn <grahn@  Oo  o.   .     .
\X/     snipabacken.se>   O  o   .

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#9626

On Sep 1, 12:34 pm, Jorgen Grahn <grahn+n...@snipabacken.se> wrote:
> On Wed, 2011-08-31, Miles Bader wrote:
> > Jorgen Grahn <grahn+n...@snipabacken.se> writes:
> >> I'm surprised you're listing g++ warning options, but omit the topical
> >> one: "-Wold-style-cast".  I use it for all my code.
>
> > The problem with -Wold-style-cast, in my experience, is that
> > system/library headers are often chock-full of C-style casts,
> > resulting in huge quantities of warnings over which one has no
> > control...
>
> Haven't seen that happen yet. Either the warning is suppressed when
> generated by a system header, or the ones I use (on Linux) happen to
> be clean.
>
> If I end up in that situation, of course I'll have to disable the
> warnings for the affected translation units.

I seem to recall some gcc command line option which is on by default
to disable warnings for system headers.

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#9649

On Sep 1, 11:37 pm, Joshua Maurice <joshuamaur...@gmail.com> wrote:

> I seem to recall some gcc command line option which is on by default
> to disable warnings for system headers.

Unsuprisingly, its -Wno-system-headers, and as you say, the default is
to suppress them.

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#9689

gwowen <gwowen@gmail.com> writes:
>> I seem to recall some gcc command line option which is on by default
>> to disable warnings for system headers.
>
> Unsuprisingly, its -Wno-system-headers, and as you say, the default is
> to suppress them.

Nonetheless, I still get tons of warnings from stuff in /usr/include,
even with -Wno-system-headers, mostly from 3rd party libraries
(typically C libraries -- which of course have no choice what type of
cast to use -- but also some C++ libraries...).

I'm not sure how it gcc distinguishes "system headers" though; the above
suggests it's not simply a test for a "/usr/include" prefix...

An instance where I get these warnings even from bona-fide system
headers is where the cast is present in a macro expansion.  E.g.,
<sys/mman.h> defines MAP_FAILED to be ((void *) -1).

-Miles

-- 
Somebody has to do something, and it's just incredibly pathetic that it
has to be us.  -- Jerry Garcia

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#9336

On 08/26/2011 02:40 PM, A wrote:
> I do not understand though reluctance to use C style casts.
>
> They can cast to reinterpret_cast but they also try out the weaker cast
> before. It is just automatic way to do what you would do manually - first
> try const_cast, then static_cast and finally reinterpret_cast... yes, it can
> use reinterpret_cast but you would have to use it anyway in a particular
> case where you really need it.
>
> So what's wrong with little automation, providing that you know what you are
> doing with casts?
>
>

C++ has many features you do not have to use. If you do not like
this part of type enforcement, then don't, just mind others working
on the same code.

I would prefer static_cast, because
- it is grepable (C-style cast is not so grepable)
- it is more strict than reinterpret_cast and C-style.
   If I (or someone else) changes the type of pThis,
   it might rightly generate an error

In both cases, it might save a lot of time otherwise spent
on debugging.

Edek

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