Delete an element from a list C++

Question

I have a problem, I'm trying to delete an element in a string list but it doesn't work for the last position. I would also like to display the position of the iterator with an arithmetic operation.

list l = {"a","b","c", "d"};

for(std::list<string>::iterator it = l.begin(); it != l.end(); it++)

    cout << " &l["<< it - l.begin() <<"]: "  << &*it << "  l["<< it - l.begin() <<"]: " <<  *it << endl;
    cout << endl;

for(std::list<string>::iterator itt = l.begin(); itt != l.end(); itt++){

    if(*itt == "d")  itt = l.erase(itt);
    cout << " &l["<< itt - l.begin() <<"]: "  << &*itt << "  l["<< itt - l.begin() <<"]: " <<  *itt << endl;
}

Thank you for your help.

Answer 1

It "doesn't work" because this line will cause itt to become the end() iterator when erasing the last element:

if(*itt == "d")  itt = l.erase(itt);

Then the for loop does itt++ before the loop condition check, and incrementing the end() iterator is undefined behavior.

You need to modify your loop like this:

for (std::list<string>::iterator itt = l.begin(); itt != l.end(); /* */) {
    if (*itt == "d") {
        itt = l.erase(itt);
    } else {
        ++itt;
    }

    // You cannot safely access *itt here because it might be l.end()
}