Thread: 2 bitwise questions

Originally Posted by kirtikjr

1. Can I access each bit of value stored in a byte?

Yes. Have at look at http://www.cs.umd.edu/class/sum2003/.../bitshift.html

Code:

#include <stdio.h>

int main () {
        int bytesw=0, unset; 
        const int A=1,B=1<<1,C=1<<2;
        
        bytesw = bytesw | A;
        printf("A set: %d\n",bytesw);
        unset = ~ A; 
        bytesw = bytesw & unset;
        printf("A unset: %d\n",bytesw);
        bytesw = bytesw | B;
        printf("B set: %d\n",bytesw);
        unset = ~ B; 
        bytesw = bytesw & unset;
        printf("B unset: %d\n",bytesw);
        bytesw = bytesw | C;
        printf("C set: %d\n",bytesw);
        unset = ~ C; 
        bytesw = bytesw & unset;
        printf("C unset: %d\n",bytesw);
        bytesw = bytesw | C | A;
        printf("AC set: %d\n",bytesw);
}

Output:

Code:

A set: 1
A unset: 0
B set: 2
B unset: 0
C set: 4
C unset: 0
AC set: 5

Originally Posted by kirtikjr

2. How does the bitwise complement (~) operators work with signed int or char? I can understand with unsigned values. Plz explain how it works with signed int or char.

I don't think that makes much difference:

Code:

#include <stdio.h>

int main() {
        char X=0;
        unsigned int alpha=6<<4, beta=3<<2, tmp;
        X = X | alpha;
        X = X | beta;
        tmp=1<<0;       // 00000001
        X = X | tmp;
        printf("%c",X);
        tmp = ~ beta;     // invert bits 00001100 to 11110011
        X = X & tmp;      //01100110 ANDED with 11110011
        tmp=10<<0;      // 00001010
        X = X | tmp;
        printf("%c\n",X);
        return 0;
}

produces the same output if you use regular signed ints.

Here's a better page: http://www.space.unibe.ch/comp_doc/c...bit_shift.html

The ~ operator does the same BITWISE operation on a signed and an unsigned operand - the operator does not care one bit about whether it is a signed or unsigned value. It just flips all the bits around to the opposite value (all zeros becomes ones, and ones become zeros).

--
mats