cppLogic errorMedium

Unexpected behavior after moving vector elements

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BugFind the bug and fix the code

What it should do

Process data by moving elements from one vector to another. Example: processDataMovedVector(src) -> dst

What happens instead

Runtime error: reading invalid memory after moving elements

#include <vector>

std::vector<int> processDataMovedVector(std::vector<int> src) {
  std::vector<int> dst;
  for (auto& elem : src) {
    dst.push_back(std::move(elem));
  }
  // src is in a valid but unspecified state here
  for (auto& elem : src) {
    std::cout << elem << " ";
  }
  return dst;
}

int main() {
  std::vector<int> src = {1, 2, 3};
  std::vector<int> dst = processDataMovedVector(src);
  return 0;
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

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#include <vector> std::vector<int> processDataMovedVector(std::vector<int> src) { std::vector<int> dst; for (auto& elem : src) { dst.push_back(std::move(elem)); } // src is in a valid but unspecified state here for (auto& elem : src) { std::cout << elem << " "; } return dst; } int main() { std::vector<int> src = {1, 2, 3}; std::vector<int> dst = processDataMovedVector(src); return 0; }

Unexpected behavior after moving vector elements

What it should do

What happens instead

More logic errors to practise

Unexpected behavior after moving vector elements

What it should do

What happens instead

More logic errors to practise