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Re: [C++ patch] Set attributes for C++ runtime library calls


On Aug 22, 2013, at 9:45 AM, Gabriel Dos Reis <gdr@integrable-solutions.net> wrote:
>> I.e. can I have something like
>> 
>> int a;
>> test()
>> {
>>  int *b=new (int);
>> }
>> 
>> with custom implementation of new that returns &a?
> 
> If the user-supplied operator new returns &a, then it must
> also ensure that 'a' is not used anywhere else -- e.g. I you can't
> do lvalue-to-value conversion on 'a' to see what is written there.

This is wrong, in the c++97 standard there is no such limitation or restriction.

> Because its storage has been reused.  That is, aliasing is framed
> in terms of object lifetime and uniqueness of ownership.

Nope, this is wrong.  Example:

int i, j;

main() {
	i = 1;
	j = i;


	i = 2;
	char *cpi = (char*)&i;
	char *cpj = (char*)&j;
	for (k= 0; k < sizeof (int); ++k)
		cpj[k] = cpi[k];
}

This is well defined.  i and j exist, as do the character objects that are pointed to by cpi and cpj.  One can use them and interleave them, they can alias, and the character objects are not unique from i and j.


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