Thread: How to get the size of an dynamic array?

I want to find out the size of ptr, i mean what is the ptr[max].

Code:

#include <iostream>

using namespace std;

int main(void) {
	int arraytest[] = { 0, 1, 2, 3, 4, 5, 6 , 7, 8 ,9};
	cout << "sizeof(arraytest): " << sizeof(arraytest) << endl; //working
	double *ptr = NULL;
	int input = 0;
	int i = 0;
	while (1)
	{
		cout << "Enter digit, 0 to end." << endl;
		cin >> input;
		if (input == 0)
		{
			break;
		}
		ptr = static_cast <double *> ( realloc(ptr, ((i + 1) * sizeof(*ptr))) );
		ptr[i] = i;
		i++;
		cout << "sizeof(*ptr): " << sizeof(*ptr) << endl; //not working, wrong size
	}
	free(ptr);
	ptr = NULL;
	return EXIT_SUCCESS;
}

For example if I would want to output all items of arraytest I could write

Code:

	for(int j = 0; j < (sizeof(arraytest) / sizeof(int)); j++) {
		cout << arraytest[j] << endl;
	}

Which in find quite generic.

For the dynamic array there is no such nice way. I could only work around and count that manually (variable i).

Is there any nice way like with sizeof?