Past-the-end iterator invalidation in C++11

Question

The most popular post on C++ Iterator invalidation rules claims that it's not clear if the past-the-end iterators (i.e., those returned by end(), cend(), rend(), and crend()) are invalidated according to the same rules as normal iterators, which point to elements in the container. These claims, made for both 2003 and 2011 C++, defer to a post discussing End iterator invalidation rules, where the accepted answer suggests that the 2003 standard is ambiguous on the matter. This conclusion is based on a comment in 23.1/10 (in the context of swap()) that seems to imply that when the spec does not explicitly mention invalidation of past-the-end iterators, they may be invalidated.

A comment on that post's question (by mike-seymour) suggests that C++11 is unambiguous on this matter, in the case of deques. My question is about all containers:

• In C++11, are there any container operations that may invalidate a past-the-end iterator, and where this behavior is ambiguous in the language specification?

Said differently,

• Can I trust the validity of a past-the-end iterator after performing a container operation that does not say it may invalidate the past-the-end iterators?

Answer 1

My question is about all containers:

• In C++11, are there any container operations that may invalidate a past-the-end iterator, and where this behavior is ambiguous in the language specification?

I am not sure what you mean with "where this behavior is ambiguous in the language specification", but there certainly are operations that invalidate past-the-end iterators (like insert into a std::vector or std::string).

Said differently,

• Can I trust the validity of a past-the-end iterator after performing a container operation that does not say it may invalidate the past-the-end iterators?

You can trust the past-the-end iterator like any other iterator: Any operation that does not (potentially) invalidate iterators won't invalidate them. Except for the possibility of the standard sporting a bug, that is all operations where it doesn't say that they (potentially) invalidate operators.

Answer 2

You should be able to trust it if the standard says the operation will not invalidate iterators. Anything else should be treated as a bug in the standard library implementation.