How to Safely Erase Elements from an STL Container Using a Reverse Iterator?

Removing an Element Using a Reverse Iterator

When working with STL containers, erasing an element using a reverse iterator can pose a challenge. By default, the erase function expects an iterator, not a reverse iterator.

To resolve this issue, there are several approaches:

1. Obtaining the Base Iterator:

The standard defines a relationship between a reverse iterator (i) and its corresponding base iterator (i.base()) as &*(reverse_iterator(i)) == &*(i - 1). This means you can obtain the base iterator by applying --() to i.base().

2. C 11-Specific Solutions:

In C 11, you have two additional options:

• std::next(i).base(): This will return the base iterator corresponding to the next element in the sequence.
• std::advance(i, 1); i.base(): This will advance the reverse iterator by one and return the base iterator corresponding to its current position.

Example Code:

for (std::list<Cursor::Enum>::reverse_iterator i = m_CursorStack.rbegin(); i != m_CursorStack.rend(); ++i) {
  if (*i == pCursor) {
    // C++11 solution
    m_CursorStack.erase(std::next(i).base());

    // Alternatively, for pre-C++11 or if desired:
    m_CursorStack.erase(--(i.base()));
    break;
  }
}

By following these approaches, you can effectively erase an element from a list using a reverse iterator while adhering to the standard's requirements.

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