c++ - Why should a shared pointer be invalidated after modification? -

according herb sutter's talk in cppcon 2015, shared_ptr should invalidated after modification,

auto sv = make_shared<vector<int>>(100); shared_ptr<vector<int>>* sv2 = &sv; vector<int>* vec = &*sv; int* ptr = &(*sv)[0]; *ptr = 1 ;  vec->push_back(2);        //a: modification *ptr = 5;                 //error: ptr invalidated "push_back" on line  ptr = &(*sv)[0]; (*sv2).reset();            //b: modification vec->push_back(6);         //error: vec invalidated "reset" on line b 

my compiler catches none of errors. anyway, use smart pointers prevent memory leakage. what's reason suppress modification of shared_ptr? avoid surprises? if case, can't declare const? on other hand, if many operations on vectorcan't applied because of share_ptr, wouldn't inconvenient?

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after reading comments, start understand here. modification of shared_ptr invalidates other raw pointers pointing it.

as dyp points out in comment, push_back might reallocate, might invalidate ptr. if doesn't reallocate, should ptr still valid? if reallocate, wouldn't simpler , more constructive if compiler carries buddies new territory, say, assigns raw pointers new address?

in greater context of things, herb advertising guidelines support library @ cppcon 2015 (he wasn't one).

the point trying make there exists code legal according standard, static analysis can tell problematic.

in example given here, have shared_ptr vector, , raw pointer pointer, , raw pointer vector held shared pointer, , raw pointer element held within vector held within shared pointer.

and did bunch of things result in undefined behavior. calls legal (call reset on shared_ptr , attempt perform operation on vector) in greater context of things, arguing compiler should able tell (via static analysis) did bad thing.

so in video see him these bad things no modern compiler catch, , demonstrate how compiler (in case visual studio 2015) imbued gsl will catch them.

the talk equally political informative. visual studio used because herb himself microsoft employee.this isn't bad thing; it's accepted visual studio great ide, , think message take away microsoft indeed committed c++, despite lot of moves in recent years demonstrated perhaps higher commitment c#, left c++ developers feeling second class citizens.