Question

I was trying to do something using sizeof operator in c++.
Please refer to the following code snippet.
http://ideone.com//HgGYB

#include <iostream>
using namespace std;
int main()
{
    int *pint = new int[5];
    int temp = sizeof(*pint);
    cout << "Size of the int array is " << temp << endl;
    return 0;
}

I was expecting the output as 5*4 = 20. Surprisingly it comes to 4. Any ideas ?

Answer 1

Here is pint is an int*. So,

sizeof(*pint) == sizeof(int)

Compiler doesn’t know about new int[5], when it does sizeof(*pint) (because sizeof() is a compile time operator).

[Note: Try the same test with statically declared array, int pint[5]; and will see the expected result.
Additionally, sizeof() returns size_t (which is an unsigned value), so it should be:

size_t temp = sizeof(...);

]