CODEWITHSUNDEEP
c++pointersvector
Rishab Balasubramanian
Rishab Balasubramanian

Reputation: 53

Is vector in c++ a pointer?

So lets say we have a vector v and I pass this to a function f

void f(vector<int> &v) {
    cout<<&v;
}

int main() {
    vector<int> v;
    v.push_back(10);  
    v.push_back(20);
    v.push_back(30);

    cout<<&v[0]<<"\n"<<&v<<"\n";
    f(v);
}

For this I get the outputs as:

0x55c757b81300
0x7ffded6b8c70
0x7ffded6b8c70

We can see that &v and &v[0] have different address. So is v a pointer that points to the start of the vector? If so, why can't I access *v? Is there a mistake I'm making?

Thanks

Upvotes: 5

Views: 3402

Answers (4)

Ranjeet R Patil
Ranjeet R Patil

Reputation: 491

std::vector is a sequence container that encapsulates dynamic size arrays. So definately, it is not a pointer.

As @tadman said, v (an instance of the vector class) does happen to contain a pointer to the start of the array.

You cannot access *v because there is no overload for the unary operator* for the class std::vector.

Upvotes: 1

user14663436
user14663436

Reputation:

No the vector in c++ is not a pointer. The vector is a class in c++

Upvotes: 0

eerorika
eerorika

Reputation: 238361

Is vector in c++ a pointer?

No. std::vector is not a pointer. It is a class.

So is v a pointer that points to the start of the vector?

No, but v (an instance of the vector class) does happen to contain a pointer to the start of the array.

why can't I access *v?

Because there is no overload for the unary operator* for the class std::vector.

Upvotes: 11

tadman
tadman

Reputation: 211610

The std::vector structure may contain additional data, such as the length. The contiguous elements are stored in a separate location and that location changes as the array is resized. &v should remain the same so long as v isn't moved, but &v[0] can be invalidated for a number of reasons.

Imagine, in very rough terms, it's:

struct vector {
  size_t size;
  T* elements;
};

The operator[] implementation takes over when you employ &v[0].

It's not a pointer, and it behaves very differently from new[].

Upvotes: 4

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