This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: -Wconversion versus libstdc++


Gabriel Dos Reis wrote:

| However, in order not to mix different issues, I think we should try
| first to resolve the much more limited issue at hand, which, I note,
| has to do with *deallocation*, not with *allocation*.

By the time we deallocate, any possible damage has already be done :-)
So, yes, you can add the casts as a temporary work-around.


Ok.

We still would not have solved the issue (I do not believe we have
separate issues).


Well, the issue with max_size vs size vs difference_type certainly we don't have anywhere, besides my private emails with Howard ;) Certainly I want to tackle it but I'm not sure whether is purely an implementation (v3) issue: I don't think the standard is very clear about the value of max_size.

About v3, note that currently, similarly to other implementations I think, in v3 container::max_size does *not* return a value directly, but essentially forwards to allocator::max_size. In general, I think the allocator should be definitely involved, because it can well decide to return sizes much smaller than numeric_limits<size_type>::max_size / sizeof(T).

In summary, for v3, one possibility could be combining the two quantities, consistently for all the containers, thus, essentially, compute container::max_size as min(allocator::max_size, numeric_limits<difference_type>::max) (all the computations modulo sizeof(T)). In this way, we could be sure that, in vector for example, substracting the _M_start and _M_finish pointers doesn't overflow a ptrdiff_t (the latter finally is casted to a size_t in order to call allocator::deallocate). Do you agree with opening a separare v3 PR and tackling it along this route?

Paolo.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]