c++ - Does iterator need to include any type information from the container by the standard? -

today came upon this question , started wonder inconsistencies between gcc/clang , visual studio.

the question general, still i'd understand - standard impose rules on whether iterator type should or should not contain container specific type information. consider snippet:

#include <unordered_map> #include <iostream>  struct hash1 {     size_t operator()(int key) const     {         return key;     } };  struct hash2 {     size_t operator()(int key) const     {         return key + 1;     }  };  int main(int argc, char** argv) {     std::unordered_map<int, int, hash1> map1;     map1[1] = 1;     std::unordered_map<int, int, hash2> map2;     map2[1] = 1;     std::unordered_map<int, int, hash2>::iterator it1 = map1.find(1);     std::unordered_map<int, int, hash2>::iterator it2 = map2.find(1);     if (it1 == it2) // visual studio 2015 gives assertion on iterator type inequality     {         std::cout << "equal";     }     else     {         std::cout << "not equal";     } } 

so in visual studio std::unordered_set iterator type std::list iterator, of course not know hash function type , can perform assignment, equality operator gives assertion since internally compares containers. gcc/clang on other hand ignore type incompatibility there no run time warnings/errors.

what standard on topic?

a pair of iterators describes sequence of values. if try 2 iterators not point @ elements of same sequence behavior of program undefined, i.e., standard doesn't impose requirements on program does.

note previous paragraph doesn't use word "container" anywhere. containers 1 way of creating sequences, not way. so, no, there no requirement iterators know containers, because iterators have no inherent connection containers.