we can initialize a vector using array. suppose,
int a[]={1,2,3}
vector<int>x(a,a+3)
this is a way . My question is, what is a and a+3 here, are they pointer?
and someone could explain this: for the above array
vector<int>x(a,&a[3])
also gives no error and do the same as above code. If we write a[3], it should be outside of the array? can someone tell me the inner mechanism?
Yes, a and a+3 are pointers. The plain a is an array that gets converted implicitly to a pointer at the drop of a hat.
The construct &a[3] is identical in meaning to a+3 for plain C arrays. Yes, a[3] is outside the array, but one-past is allowed to point to, if you don't dereference it.
A vector's range constructor looks like this:
template <class InputIterator>
vector (InputIterator first, InputIterator last,
const allocator_type& alloc = allocator_type());
It will construct elements in the range [first, last), meaning that the last element is not included. &a[3] points to an element outside the bounds of the array, similar to how std::end(a) will point one past the end of a. Compare it to:
std::vector<int> x(std::begin(a), std::end(a));
Also, *(a + 3) is equivalent to a[3].
int a[]={1,2,3}
vectorx(a,a+3)
a is an array so it is always pointing to its base address. a+3 mean base address+(sizeof(int) *3)
suppose base address is 100 a=100; a+3=106;
