Question

I know that if the integer is dissected rather than being computed as a whole, the total of individual bytes will yield incorrect result. However, for curiosity, I want to examine individual byte and make.I’m not sure if this is correct to inspect each byte in an integer pointer:

#include <iostream>
int main(int argc, char *argv[])
{
    using namespace std;

    int *num = new int;
    *num = 123456789;
    cout << "Num: " << *num << '\n';
    char* numchar_ptr = reinterpret_cast<char*> (num);
    for (int i = 0; i < 4; ++i)
    {
        cout << "number char: " << i << ' ' << (short) *(numchar_ptr+i) << '\n';
        *(numchar_ptr+i) = i
    }
    cout << "New num: " << *num << '\n';
    delete num;

    return 0;
}

According to the loop, the bytes in the integer will be: 0 1 2 3
which is equal to 00000000 00000001 00000010 00000011 in binary and 66051 in decimal
But I got the result “New num” is 50462976. Why?

Answer 1

You need to take endianness into account. On your system, numbers are stored in little-endian representation, which means that the lowest-addressed byte is the least-significant.

Therefore, your number is:

  0 * (1 << 0)
+ 1 * (1 << 8)
+ 2 * (1 << 16)
+ 3 * (1 << 24)

which is 50462976.