Question

I was going through the existing code and when debugging the UTC time which is declared as

unsigned int utc_time;

I could get some positive integer every time by which I would be sure that I get the time. But suddenly in the code I got a negative value for the variable which is declared as an unsigned integer.

Please help me to understand what might be the reason.

Answer 1

Unsigned integers, by their very nature, can never be negative.

You may end up with a negative value if you cast it to a signed integer, or simply assign the value to a signed integer, or even incorrectly treat it as signed, such as with:

#include <stdio.h>

int main (void) {
    unsigned int u = 3333333333u;
    printf ("unsigned = %u, signed = %d\n", u, u);
    return 0;
}

which outputs:

unsigned = 3333333333, signed = -961633963

on my 32-bit integer system.