Question

Given a particular stl collection in C++, is the end() value equivalent for all instances of the same templatization? In other words, will the following work for all stl containers and circumstances (not just for std::map)?

std::map<Key, Value> foo(int seed);

std::map<Key, Value> instance1 = foo(1);
std::map<Key, Value> instance2 = foo(2);
std::map<Key, Value>::iterator itr = instance1.begin();
std::map<Key, Value>::iterator endItr = instance2.end(); // Comes from other collection!

for (; itr != endItr; ++itr) {
  // Do something on each key value pair...
}

Answer 1

No, because of the STL container and iterator requirements:

23.2.1 General container requirements [container.requirements.general]

6 begin() returns an iterator referring to the first element in the
container. end() returns an iterator which is the past-the-end value
for the container. If the container is empty, then begin() == end();

24.2.1 In general [iterator.requirements.general]

6 An iterator j is called reachable from an iterator i if and only if
there is a finite sequence of applications of the expression ++i that
makes i == j. If j is reachable from i, they refer to elements of the
same sequence.

The equality of begin() and end() for empty containers means that begin() and end() need to be part of the same container objects, and hence end() cannot be a static member of a container class. Note also that -except for forward iterators- applying operator-- on end() would be impossible to resolve with a static end() iterator.