Thread: Bitwise Operators

I'm having trouble with these little buggers. I know how to turn certain bits on, but I can't work out the operator to turn them off. Eg:

Code:

int integer;
integer=45;
integer|=1|4|8; //Ensures that these bits are on
integer?=2|16; //Ensures that these bits are off

What I want is the symbol where the question mark is. What code can I use to ensure that certain bits are turned off?

Okay, I searched, and I found an article by some self-righteous dude who actually said the right stuff then got the code wrong. This was the article: Bitwise Operators

For clearing a bit, he had the right theory, but when he showed an example, he must have made a few typos. But this is how I am clearing a bit now:

Code:

int integer;
integer=11;
integer&=(~8);

Is this the best way to do it?

For example:

I have a number 11. So its binary form will be as follows:

Bits : 0 0 0 0 1 0 1 1
Bit Number : 7 6 5 4 3 2 1 0

Now suppose I want to turn off 3th bit.

So I have to do bitwise AND (&) operation with following Number

Number(Bits) : 1 1 1 1 0 1 1 1
Bit Number : 7 6 5 4 3 2 1 0


So result of two number will be

0 0 0 0 1 0 1 1 (11)
& 1 1 1 1 0 1 1 1 (247)
-----------------------
0 0 0 0 0 0 1 1 (3)

So programatically you can do like this:

{
unsigned char c1 = 11;
unsigned char c2 = 247;
unsigned char c3 = c1 & c2;
}

So c3 will be 3.

I don't know, cr_naik, I think Salem's method and my method are a bit easier to use. But hey, do it your way if it makes you happy.

You can also try to use the bitset class but it may be overkill depending on what you want to do with it.

Code:

#include <bitset>
#include <limits>
#include <iostream>
using namespace std;

int main()
{
    bitset<numeric_limits<int>::digits> bits(45);

    cout << "bits is: " << bits << endl;

    bits.set(1);        // Turn on bit 1
    bits.set(4);        // Turn on bit 4
    bits.set(8);        // Turn on bit 8

    bits.reset(2);      // Turn off bit 2
    bits.reset(16);     // Turn off bit 16, no effect since it is already 0

    cout << "bits is: " << bits << endl;

    return 0;
}

Outputs:
bits is: 00000000000000000000000000101101
bits is: 00000000000000000000000100111011