The output of the last list element does not occur

Question

My task is to display the first and last elements of the list. I have iterators that point to the first and last element of a list. With their help, I am trying to implement a task. Everything works with the first element, with the last - the program crashes. What could be the problem?

typedef list<float>::iterator it;
it i = X.begin(); it j = X.end();
cout << "First element -->> " << *i << "\tLast element -->> ";
cout << *j << endl;

Answer 1

According to the docs:

end Returns an iterator pointing to the past-the-end element in the sequence

This element does not exist, so you can't access it. But it allows you to iterate nicely (using < for comparison, not <=):

for (it = X.begin(); it < X.end(); ++it)
    // do stuff

Answer 2

The functions begin() and end() define a half open range([begin, end)), which means: The range includes first element but excludes the last element. Hence, the name past the end.

See this answer for The advantage of an half open range.

Have a look at cppreference. To print the last element, try this:

typedef list<float>::iterator it;
it i = X.begin(); it j = X.end();
cout << "First element -->> " << *i << "\tLast element -->> ";
cout << *(j - 1) << endl;

Or

A better option would be rbegin().

typedef list<float>::iterator it;
it i = X.begin(); it j = X.rbegin();
cout << "First element -->> " << *i << "\tLast element -->> ";
cout << *j << endl;