Segmentation fault caused by repeating pop_back() and push

When I run the following code in Clion(an IDE) with c 11. I ran into a segmentation fault. But if I delete the if statement, add else before pop_back, remove push_back, or remove pop_back(do them separately). There would be no error. So why there would be a segmentation fault and why doing any of the above would eliminate the error?

#include "vector"
using namespace std;

int main() {
    vector<int> test;
    for(int i = 0; i < 10000; i  ){
        if(i % 2 == 0)
            test.push_back(i);
        test.pop_back();
    }
}

Edit: Some people say it's because pop_back from empty vector, but if I remove push_back() there won't be any problem(even if I push_back some elements before the loop).

CodePudding user response：

You are popping from the vector when it is empty. Using pop_back() from an empty vector results in undefined behaviour which means:

your program could crash
your program could print some nonesens
your program could continue normally
your program could continue normally, but have some other strange seemingly unrelated behaviour later
or some other behaviour

Consider this code:

#include <vector>
#include <iostream>

using namespace std;

int main() {
  vector<int> test;
    
  for (int i = 0; i < 10; i  ) {
    if (i % 2 == 0)
      test.push_back(i);

    if (test.empty())
      cout << "stack is empty" << endl;
    else
      test.pop_back();
  }
}