I mean what's the difference between vector<int> v; and vector<int> *v = new vector<int>;

I mean what's the difference between vector<int> v; and vector<int> *v = new vector<int>;

In the second case you create it on heap, and need to delete it manually. In my opinion should use the first case whenever possible.

Even the first is allocated in heap.

Nope.. well.. the data is allocated on heap, but the vector itself not (well, that depends too), I don't know what is inside the vector class, there are probably size and a pointer to the data. And in the first case you create the vector on stack if it's local variable (so these two values are on stack), or it's part of the class if it's a member of a class (so the data for the vector is allocated with the class). In the second case you create the vector on heap always and have a pointer to the vector.

(so these two values are on stack - you mean pointer and size?

Nope.. well.. the data is allocated on heap, but the vector itself not (well, that depends too), I don't know what is inside the vector class, there are probably size and a pointer to the data. And in the first case you create the vector on stack if it's local variable (so these two values are on stack), or it's part of the class if it's a member of a class (so the data for the vector is allocated with the class). In the second case you create the vector on heap always and have a pointer to the vector.

In the second case you create the vector on heap always and have a pointer to the vector. - the pointer is in the stack ?

The second is also can be bad for performance btw, because compiler is forced to fetch vector from RAM just to fetch more data from RAM.

I meant the pointer that you get from new

Didn't get this statement. Everything is allocated in RAM - stack, heap. So what do you mean by explicit fetching from RAM?

That's a deep topic. Not sure you need it right now. To make it short and simple, traversing a pointer sometimes can be slow, because processor needs to wait the data transferred from RAM (if it doesn't have it on caches already). But compilers can reorder operations to fill the processor with useful work while it's waiting for the data. But if you traverse a pointer just to get another pointer to traverse that's harder to improve and there are more chances that processor will be just waiting. But again, that's a deep topic, and everything is more complicated in reality.

That's a deep topic. Not sure you need it right now. To make it short and simple, traversing a pointer sometimes can be slow, because processor needs to wait the data transferred from RAM (if it doesn't have it on caches already). But compilers can reorder operations to fill the processor with useful work while it's waiting for the data. But if you traverse a pointer just to get another pointer to traverse that's harder to improve and there are more chances that processor will be just waiting. But again, that's a deep topic, and everything is more complicated in reality.

So in general, std:: vector generates overhead?

But I'm talking about a vector created with new

I mean what's the difference between vector<int> v; and vector<int> *v = new vector<int>;

So in general, std:: vector generates overhead?

Every thing generates overhead. So what?

Basically traversing pointers will generate overhead right. Pointers are not in python, then why it's slower than c++

Well, actually python uses pointers much more heavily under the hood, afaik

Basically traversing pointers will generate overhead right. Pointers are not in python, then why it's slower than c++

What is slower?

These are different classes of memory this std::vector object belongs to . The later is Dynamic , the first one is unknown depending on the place where declaration took place

Usage of pointers.

But, for the first one too the data is present in the heap

But, for the first one too the data is present in the heap

But, for the first one too the data is present in the heap

Nope.. well.. the data is allocated on heap, but the vector itself not (well, that depends too), I don't know what is inside the vector class, there are probably size and a pointer to the data. And in the first case you create the vector on stack if it's local variable (so these two values are on stack), or it's part of the class if it's a member of a class (so the data for the vector is allocated with the class). In the second case you create the vector on heap always and have a pointer to the vector.

What's the difference when you say that the vector is NOT allocated in heap in the first(you said it depends) and in the second case the vector is allocated in heap ALWAYS. I mean, what is vector that you are refering to? Is it the data or IDK what?

Not the data, the object of std::vector

With the default allocator - yes.

Not the data, the object of std::vector

so, you mean the object in the first case is present in the stack and the object in the second case is present in the heap?

What's the difference when you say that the vector is NOT allocated in heap in the first(you said it depends) and in the second case the vector is allocated in heap ALWAYS. I mean, what is vector that you are refering to? Is it the data or IDK what?

so, you mean the object in the first case is present in the stack and the object in the second case is present in the heap?

It is useless to argue here, the vector itself can be allocated as any memory class, and the data of vector also can be allocated differently depending on allocator

So, when the object is present in the stack and gets destroyed, automatically the destructor is called and deallocates the entire data from the heap?

Why is this so important to you?

IDK, I think I should know this.

It is useless to argue here, the vector itself can be allocated as any memory class, and the data of vector also can be allocated differently depending on allocator

what's the default implementation?

the vector itself can be allocated as any memory class. what does that mean

You know memory clases in c and c++? Auto, static, global etc

You know memory clases in c and c++? Auto, static, global etc

I mean NO.😹

I checked it. yes I know

Beautiful!

I didn't know that we call them memory classes.🤦‍♀️

Doesn't multimap provide the use of [] operator?

any function to check that?

You want to check that there's a pair of key-value that contains {A, B}?

You want to check that there's a pair of key-value that contains {A, B}?

It will be much better. aint it?