c++ - Does push_back in vector insert at the same location? - 


class example {     public: int i;     example(const example &e)     {         = e.i;     }     example(int i)     {         this->i = i;     } };  int main() { std::vector<example*> vec; std::vector<example*> newvec;  example* ex1 = new example(1); example* ex2 = new example(2);  vec.push_back(ex1); vec.push_back(ex2);  //newvec = vec; --> shallow copy  for(int i=0; i<vec.size(); ++i) // --> deep copy {     example newe(*(vec[i]));     newvec.push_back(&newe); }  for(int i=0; i<newvec.size(); ++i) {     std::cout << "\nfoobar" << newvec[i]->i << "\n"; } }

the above code prints foobar2 twice. shouldn't print foobar1 , foobar2? also, best way copy vector containing objects? want deep copying.

for(int i=0; i<vec.size(); ++i) // --> deep copy {     example newe(*(vec[i]));     newvec.push_back(&newe); }

in code make copy of vec[i] example newe. push_back address of newe newvec vector. newe object goes out of scope , destroyed, end having pointer garbage inside newvec.

if want deep copy of vector content, and want store owning pointers objects, consider using vector of smart pointers, e.g. vector<shared_ptr<example>>.

in case, can copy vectors operator=, , reference counts of shared_ptrs automatically updated.

yoy may want consider simpler design of having vector<example> (without pointer indirection).


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