Question

This states I can construct a vector from an array as follows:

// the iterator constructor can be used to construct from arrays:
int myints[] = {16,2,77,29};
vector<int> myvector (myints, myints + sizeof(myints) / sizeof(int) );

Why is the constructor’s second argument myints + sizeof(myints) / sizeof(int)?

Answer 1

The expression sizeof(myints) / sizeof(int) gets the number of elements in the myints array.

myints gets a pointer to the first element of the array.

So the expression myints + sizeof(myints) / sizeof(int) is a pointer one past the end of the myints array, which is what the two-iterator constructor of std::vector expects. This creates a vector with a copy of all the elements in the original array.

Bear in mind that pointers are iterators, so the above is equivalent to

vector<int> myvector (std::begin(myints), std::end(myint));