The Big Programming Thread - Page 294

I suspect an out-of-bounds error: a std::vector does not have any "space" upon construction - its size dynamically grows as you need to add new stuff to it (or shrinks if you're taking things out of it).

heap[1] = item(k, e)

heap[1] is out-of-bounds because there isn't a [1] in heap.

std::pair<int, std::string> item(5, "apple pie");
std::vector<std::pair<int, std::string> > heap;
heap.push_back(item);

The "push_back()" function adds an object to the heap. After having added the item, you can now access it as "heap[indexNumber]" - in this case, "heap[0]" will let you access (5, "apple pie"). Alternatively:

std::vector<item> heap(10)

This will leave you with 10 default-constructed items (in this case, pairs of ints and strings).

std::cout << heap[0].second << '\n'; //will print "apple pie"
std::cout << heap[1].second << '\n'; //undefined behavior if the size of heap is less than 2
std::cout << heap.at(0).second << '\n'; //will also print "applie pie"
std::cout << heap.at(1).second << '\n'; //will throw an out-of-bounds exception, so you aren't confused

The at() function can help alleviate this problem.

A useful resource on vectors is here, in case you have other issues.

friend Fraction operator+ (int i, Fraction& f1);
friend Fraction operator+ (Fraction& f1, int i);