CODEWITHSUNDEEP
c++arraysvector
lukai
lukai

Reputation: 566

Vector initialization using array

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?

Upvotes: 0

Views: 84

Answers (4)

Rustam
Rustam

Reputation: 6515

vectorx(a,&a[3])

Here &a[3] is equivalent to a+3

Upvotes: 0

Rustam
Rustam

Reputation: 6515

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;

Upvotes: 0

JDługosz
JDługosz

Reputation: 5642

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.

Upvotes: 3

user3920237
user3920237

Reputation:

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].

Upvotes: 0

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