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Re: operator new returns nonzero


On Sep 7, 2013, at 1:03 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
> On Sat, 7 Sep 2013, Mike Stump wrote:
> 
>> 
>> On Sep 7, 2013, at 12:37 PM, Gabriel Dos Reis <gdr@integrable-solutions.net> wrote:
>> 
>>> On Sat, Sep 7, 2013 at 2:27 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
>>>> On Sat, 7 Sep 2013, Mike Stump wrote:
>>>> 
>>>>> On Sep 7, 2013, at 3:33 AM, Marc Glisse <marc.glisse@inria.fr> wrote:
>>>>>> 
>>>>>> this patch teaches the compiler that operator new, when it can throw,
>>>>>> isn't allowed to return a null pointer.
>>>>> 
>>>>> 
>>>>> You sure:
>>>>> 
>>>>> @item -fcheck-new
>>>>> @opindex fcheck-new
>>>>> Check that the pointer returned by @code{operator new} is non-null
>>>>> before attempting to modify the storage allocated.  This check is
>>>>> normally unnecessary because the C++ standard specifies that
>>>>> @code{operator new} only returns @code{0} if it is declared
>>>>> @samp{throw()}, in which case the compiler always checks the
>>>>> return value even without this option.  In all other cases, when
>>>>> @code{operator new} has a non-empty exception specification, memory
>>>>> exhaustion is signalled by throwing @code{std::bad_alloc}.  See also
>>>>> @samp{new (nothrow)}.
>>>>> 
>>>>> ?
>>>> 
>>>> 
>>>> Thanks, I didn't know that option. But it doesn't do the same.
>>> 
>>> Indeed.
>> 
>> Can this throw:
>> 
>> void *operator new (long unsigned int s) {
>> return 0;
>> }
>> 
>> ?  Is this allowed to return 0?
> 
> I think using this function is illegal.

Yes, according the the standard, and without any compilation flags, it is.

However, with -fcheck-new and in the g++ language, it is not.

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