C++：在 push_back 时迭代指针向量时出现分段错误

Question

I want to iterate through a vector of pointers pointing on objects. While iterating, I have to push_back new pointers to the vector. Before the loop, the number of push_backs is unknown and there is no abort criterion, so that I can't use a while loop.

Here is an example using pointers on integers, that shows the same error as the version with objects: Segmentation fault (core dumped) after one iteration.

vector<int*> vec;
int a = 43;
vec.push_back(&a);

for (vector<int*>::iterator it = vec.begin(); it != vec.end(); ++it) {
    cout << *(*it) << " " << *it << endl;
    vec.push_back(&a);
}

The same Code but with integers works great.

vector <int>vec;
int a = 43;
vec.push_back (a);

for (vector < int >::iterator it = vec.begin (); it != vec.end (); ++it){
    cout << (*it) << " " << *it << endl;
    vec.push_back (a);    
}

Answer 1

push_back invalidates the iterator when appending results in size > capacity so it reallocates and copies to the new space.

Appends the given element value to the end of the container.

1) The new element is initialized as a copy of value.

2) value is moved into the new element.

If the new size() is greater than capacity() then all iterators and references (including the past-the-end iterator) are invalidated. Otherwise only the past-the-end iterator is invalidated.

Plus as @Jesper pointed out you are storing a reference to a local variable in your vector :

int a = 43; 
vec.push_back(&a);

which if went out of scope before your vector you will have dangling references.