Vector gives 0 as output when out of bounds?

Question

I was playing around with nested vectors and printing random elements to see the output and I noticed that when I go out of bounds I don't get an error. I simply get 0 returned as the value.

Why is this?

Is the vector being resized and initialized to zero whenever I attempt to call an out-of-bounds element by index?

Here's the code I was running:

#include <iostream>
#include <vector>


int main(){
  std::vector<std::vector<int>> matrix;
  std::vector<int> temp;
  temp.push_back(1);
  temp.push_back(2);
  matrix.push_back(temp);
  std::cout << matrix[0][45] << std::endl;

  return 0;
}

score 1 · Answer 1 · answered Apr 25 '17 at 19:49

1

You're having undefined behavior, that it prints 0 is just a mere coincidence.

answered Apr 25 '17 at 19:49

deW1

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Thanks! Is there anyway that I can make it give me an error? – somerandomdude Apr 25 '17 at 19:50
@Hadi check the boundaries and respond accordingly – deW1 Apr 25 '17 at 19:52
1

@Hadi Use `at()` instead of `[]`: `vector.at(0)` – Justin Apr 25 '17 at 19:53
1

@Hadi `matrix.at(0).at(45)` – user4581301 Apr 25 '17 at 19:53
`at` will throw an exception but I'd still check boundaries instead. (where applicable at least) – deW1 Apr 25 '17 at 19:55

Vector gives 0 as output when out of bounds?

1 Answers1