Thread: bit modifier in structure

Hello Everyone,

Somewhere on web, I got this code example of structure (I don't remember but it was something like the snippet below):

Code:

#include <stdio.h>
#include <stdlib.h>


typedef struct str
{
unsigned int first:1;
int second:1;


}str;


int main()
{
    str exp;
    exp.first=1;
    exp.second=1;


    printf("%d %d\n", exp.first,exp.second);




    exp.first=-1;
    exp.second=-1;

    printf("%d %d\n", exp.first,exp.second);

    return 0;
}

Both the printf prints

1 -1

Could you please explain why. This may look because of "signed"(as it is obvious) but I failed to get any explanation for why "exp.second" prints "-1" at first print statement !!

Thanks in advance

A 1-bit unsigned int can only ever be 0 or 1.
A 1-bit signed int can only ever be 0 or -1 (the single bit IS the sign bit).