why there is a integer overflow in this multiplication? [duplicate]

Question

I am puzzled on this code snippet:

#include <climits>
#include <iostream>
int main(void) {
    using namespace std;
    cout << "long max " << LONG_MAX << endl;
    long x = 2 * 1024 * 1024 * 1024;
    cout << "2 * 1024 * 1024 * 1024 = " << x << endl;
    return 0;
}

I was expecting 2147483648 as it should be, instead I am getting. Using unsigned doesn't seem to help. what gives?

long max 9223372036854775807
2 * 1024 * 1024 * 1024 = -2147483648

Answer 1

Add some Ls*. long x = 2L * 1024L * 1024L * 1024L;

(Technically, as long as one literal is of type long the others will be promoted to long)

The overflow happens because 2, etc. is of type int by default and the overflow happens before the assignment.

See integer literals which explains the different literals.