length of dynamic array in c++

Question

Possible Duplicate:
How to find the sizeof(a pointer pointing to an array)

I declared a dynamic array like this:

int *arr = new int[n];   //n is entered by user 

Then used this to find length of array:

int len = sizeof(arr)/sizeof(int);

It gives len as 1 instead of n . Why is it so?

Solution 1

Because arr is not an array, but a pointer, and you are running on an architecture where size of pointer is equal to the size of int.

Solution 2

Because sizeof does not work for dynamic arrays. It gives you the size of pointer, since int *arr is a pointer

You should store the size of allocated array or better use std::vector