How Can I Erase an Element from a List Using a Reverse Iterator in C ?

Erasing an Element from a List Using a Reverse Iterator

It is possible to encounter a scenario where you wish to remove an element from a list using a reverse iterator, but the erase() function only accepts a regular iterator. This can pose a challenge, as converting a reverse iterator to a regular iterator is not straightforward.

Solution:

The key to resolving this issue lies in understanding the relationship between a reverse iterator and its base iterator. According to the C Standard, the base iterator of a reverse iterator i is &*(i - 1). This means that to obtain the base iterator, we decrement i.

Example:

Consider the following code snippet:

for ( std::list< Cursor::Enum & >::reverse_iterator i = m_CursorStack.rbegin(); i != m_CursorStack.rend(); ++i )
{
    if ( *i == pCursor )
    {
        m_CursorStack.erase( --(i.base()) );
        break;
    }
}

In this example, the base iterator is obtained by decrementing i.base(). By passing this base iterator to the erase() function, we can successfully remove the desired element from the list.

C 11 Solutions:

For C 11 and later, two additional solutions are available:

1. Using std::next():

m_CursorStack.erase( std::next(i).base() );

This solution remains unchanged, while std::next() is used to advance the reverse iterator one position forward, effectively retrieving its base iterator.

2. Advancing the Reverse Iterator:

std::advance(i, 1);
m_CursorStack.erase( i.base() );

In this solution, the reverse iterator is advanced one position using std::advance(), which effectively aligns its base iterator with the desired element for erasure.

Whichever solution you choose, these approaches provide clean and straightforward methods for erasing elements from a list using a reverse iterator.

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