C++ code works fine on desktop but not on the laptop

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This simple code for some reason works perfectly fine on my desktop but when I try it on my laptop only the first part (printing the elements of vector) works then the program ends and instead of saying "Process finished with exit code 0" it says
"Process finished with exit code -1073741819 (0xC0000005)". I don't know what's wrong with my laptop. Can anyone help me?

#include <iostream>
#include <vector>

using namespace std;

int main() {
    vector<int> array{1, 2, 3, 4, 5};
    vector<int>::iterator it;
    int arraysize;
    for (int i = 0; i < array.size(); i++) {
    cout << array[i] << endl;
    }
    cout << " " << endl;

    for (it = array.begin(); it < array.end(); it++) {
        if(*it%2==0){
            array.erase(it);
            it--;
        }
    }
    arraysize=array.size();
    cout<<"size:"<<arraysize<<endl;
    for (int i = 0; i < array.size(); i++) {
        cout << array[i] << endl;
    }



    return 0;
}
c++
asked on Stack Overflow Jun 24, 2020 by Draxes

4 Answers

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This happens because of iterator invalidation, when you erase an element of the vector the iterator it becomes invalidated leading to undefined behaviour, you can read more about this here Iterator invalidation rules

answered on Stack Overflow Jun 24, 2020 by SzymonO
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The problem is not with the computer but with the code.

array.erase(it); invalidates the iterator it, and any subsequent use of it has undefined behaviour.
The worst kind of undefined behaviour is the one that appears to work.

erase returns an iterator to the element after the erased one, and you should use that.

for (it = array.begin(); it < array.end(); it++) {
    if(*it%2==0){
        it = array.erase(it);
        it--;
    }
}

or

it = array.begin(); 
while (it < array.end()) {
    if(*it%2==0){
        it = array.erase(it);
    }
    else {
        it++;
    }
}
answered on Stack Overflow Jun 24, 2020 by molbdnilo
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Your program has undefined behaviour, you decrement an invalid iterator

array.erase(it); // it becomes invalid
it--; // Undefined

You can avoid this by removing elements with the "erase-remove" pattern

auto is_even = [](int i) { return i%2==0; };
array.erase(std::remove_if(array.begin(), array.end(), is_even), array.end());

Or in C++20

std::erase_if(array, is_even);
answered on Stack Overflow Jun 24, 2020 by Caleth • edited Jun 24, 2020 by Caleth
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There is nothing wrong with your laptop. The problem is with the code. When you erase something from the vector, it invalidates the preexisting iterators following the erased elements. You may want to use the return value of erase, which references the new reallocated location of the erased element's successor.

answered on Stack Overflow Jun 24, 2020 by lukeg • edited Jun 24, 2020 by lukeg

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