Bitfields Unexpected Output
I have a code that goes like this:
typedef struct _point {
int x:2;
int y:2;
}Point;
int main()
{
Point p;
p.x = 2;
printf("%d\n", p.x);
}
The output produced is -2 but I was expecting a 2. Please help
typedef struct _point {
int x:2;
int y:2;
}Point;
int main()
{
Point p;
p.x = 2;
printf("%d\n", p.x);
}
The output produced is -2 but I was expecting a 2. Please help
In 2's compliment, the high bit is negative. Therefore if you have a 2-bit value, its range is [-2..1]. If you want the range to be [0..3], then you must make the variable unsigned:
|
|
Classical sign extension bug.
x can only contain two bits, to which you're assigning binary 10. When you pass p.x to printf(), the value is converted to int and sign extension is applied: 10b becomes 11111111 11111111 11111111 11111110b (assuming 32-bit ints), which in two's complement is -2.
If you want to be able to store 2, either using unsigned instead of int, or give at least three bits to each member.
x can only contain two bits, to which you're assigning binary 10. When you pass p.x to printf(), the value is converted to int and sign extension is applied: 10b becomes 11111111 11111111 11111111 11111110b (assuming 32-bit ints), which in two's complement is -2.
If you want to be able to store 2, either using unsigned instead of int, or give at least three bits to each member.
Topic archived. No new replies allowed.