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From: "Bo Persson" <bop@gmb.dk>
Newsgroups: comp.lang.c++
Subject: Re: removing constness of a true const
Date: Sat, 16 Jul 2011 08:32:10 +0200
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Victor Bazarov wrote:
> On 7/14/2011 5:33 PM, Bo Persson wrote:
>> siddhu wrote:
>>> On Jul 14, 1:05 pm, "Balog Pal"<p...@lib.hu>  wrote:
>>>> "siddhu"<siddharth....@gmail.com>
>>>>
>>>>> I guess removing constness of a true const( I guess it is also
>>>>> called bitwise const ) using const_cast is undefined behavior.
>>>>> Can you please give an example of a true const and may be a
>>>>> sample code which exhibits undefined behavior by removing
>>>>> constness of a true const.
>>>>
>>>> Removing constness is well defined. But actually modifying
>>>> non-mutable member of a const object is UB. By any means,
>>>> including the use of pointer/ref from const_cast.
>>>
>>> Thanks Balog!
>>> Does that mean removing constness of 'this' in const member
>>> function is an UB?
>>
>> It is if the object is really const.
>>
>> Suppose the data is stored in a ROM. What happens when you try to
>> change it?
>
> I see two concepts here, removing of 'const' and changing.  I don't
> think that the former is the same as the latter, or is it?
>
> V

Right, casting away const as such is ok, as long as you don't use it 
for anything non-const.

My point was more that class objects can very well be read-only. 
Trying to change them will then have an undefined result.



Bo Persson