How to Safely Remove Elements from a Vector During Iteration in C ?

Remove Elements from a Vector Within a Loop

When iterating through a vector, there may be scenarios where you need to remove elements based on certain criteria. However, attempting to modify the vector while iterating can lead to runtime errors.

Consider the following scenario:

for (vector<Player>::iterator it = allPlayers.begin(); it != allPlayers.end(); it++) {
  if (it->getpMoney() <= 0)
    it = allPlayers.erase(it);
  else
    ++it;
}

This code intends to remove players with zero or negative money. However, it fails with an error related to the assignment operator. To resolve this issue, avoid incrementing the iterator within the loop. Instead, rely on the iterator returned by the erase() function.

for (vector<Player>::iterator it = allPlayers.begin(); it != allPlayers.end(); /*it++*/) {
  if (it->getpMoney() <= 0)
    it = allPlayers.erase(it);
  else
    ++it;
}

Furthermore, the use of operator= by the erase() function requires the Player class to be assignable, meaning the Player class must implement an assignment operator.

Erase-Remove Idiom for Vector Manipulation

To simplify the task of removing elements from a vector, embrace the Erase-Remove Idiom:

allPlayers.erase(
  std::remove_if(
    allPlayers.begin(),
    allPlayers.end(),
    [](Player const &amp; p) { return p.getpMoney() <= 0; }
  ),
  allPlayers.end()
);

This idiom combines the remove_if() algorithm to identify the elements to erase and the erase() method to remove the required range.

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