c++ help

Relevant code:
void LogFormatter::debug() {
    cout << contents.Get_postByIndex(13).Get_lines(0) << endl; // outputs "..."

    contents.Get_postByIndex(13).delLine(0);

    cout << contents.Get_postByIndex(13).Get_lines(0) << endl; // outputs "..."
}

void Post::delLine(int which) {
    cout << lines[which] << endl; // outputs "..."
    lines.erase(lines.begin() + which);
    cout << lines[which] << endl; // outputs "((sorry, got distracted))"
}

Output:

...
...
((sorry, got distracted))
...