Why Does Erasing Elements from a Vector with an Iterator and Incrementing it in a For Loop Cause a Crash?

Vector erase iterator and its unexpected behavior

In the provided code snippet, the for loop uses res.erase(it) to erase elements from the vector res, then increments it in the same loop. However, this leads to unexpected behavior and a crash.

The code employs a vector iterator it, which points to the current element being processed. The res.erase(it) function erases the element pointed to by it and returns an iterator pointing to the next element in the vector. In the provided code, the loop continues to use this returned iterator, even if it points to the end of the vector (.end()).

Random access iterators, such as the one used here, cannot be incremented past the end of the sequence they belong to. Thus, incrementing .end() in the loop leads to a crash.

To resolve this issue, the for loop should be modified to use a while loop instead of relying on the automatic increment provided by the for loop:

while (it != res.end()) {
  it = res.erase(it);
}

This approach ensures that the loop continues until it reaches the end of the vector, and it correctly skips erased elements without the risk of crashing due to invalid iterator increment operations.

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