Cannot dereference end list iterator - c++

Question

I'm currently working on a project about browser histories. I'm using the STL's list implementation to keep track of the different websites. I have most of it figured out but I can't seem to resolve the error:
Screenshot; cannot dereference end list iterator.
The website data is contained within my Site objects.
class BrowserHistory {
private:
list<Site> history;
list<Site>::iterator current = history.begin();
public:
void visitSite(string, size_t)
void backButton();
void forwardButton();
void readFile(string);
};
void BrowserHistory::visitSite(string x, size_t y)
{
while (current != history.end()) {
history.pop_back();
}
history.push_back({ x, y });
current++;
}
void BrowserHistory::backButton()
{
if (current != history.begin())
current--;
}
void BrowserHistory::forwardButton()
{
if (current != history.end())
current++;
}
void BrowserHistory::readFile(string filename)
{
string action, url;
size_t pageSize;
ifstream dataIn;
dataIn.open(filename);
while (!dataIn.eof()) {
dataIn >> action;
if (action == "visit") {
dataIn >> url >> pageSize;
history.push_back({ url, pageSize });
current++;
}
if (action == "back") {
current--;
}
if (action == "forward") {
current++;
}
}
dataIn.close();
}
Can anyone explain to me what's wrong? Thanks in advance for any help.

Answer 1

When you initialise current, the list is empty.
Adding elements to the list does not suddenly make it a valid iterator, even though it will be different from end.
It looks like you're thinking of iterators as very much like pointers, but they're not.
Iterators are for iterating and should be considered transient, and not stored for later use.
Use a vector, and use an index for current instead of an iterator.
Further, I would rename the "button" functions (what does the history care about buttons?) to "goBack" and "goForward" and use your actual interface when reading:
void BrowserHistory::readFile(string filename)
{
ifstream dataIn(filename);
string action;
while (dataIn >> action) {
if (action == "visit") {
string url;
size_t pageSize;
if (dataIn >> url >> pageSize) {
visitSite(url, pageSize);
}
else {
// Handle error
}
}
else if (action == "back") {
goBack();
}
else if (action == "forward") {
goForward();
}
else {
// Handle error
}
}
}