Get a bit value from a specific position

We have this binary number 0b101011, and we want to extract the bit value from the 3rd position from the right side.

Binary number 1 0 1 0 1 1
Position from right 5 4 3 2 1 0 
  0b101011;
      ^ Bit to extract

The first thing we need is a mask. For position 3, the mask would be 0b001000. We can generate the value using the left shift (<<).

int bitMask = 1 << 3; // This will generate the number 0b001000

Using the Bitwise AND operator (&), we will get 0b001000 or 0b000000, which depends on the value of the bit. In the current example at position 3 for the number 0b101011, we will get 0b001000.

  0b101011
& 0b001000
  ________
  0b001000

After we get the value from the AND operation, we only need to use the right shift (>>) to bring the bit to the zeroth position.

  0b001000 >> 3 = 0b000001

Sample code,

int number = 0b101011;
int position = 3;

int bitMask = 1 << position;

int masked = number & bitMask;

// The result will have a value of 1 or 0 based on the bit value from the number
// at the specific position
int result = masked >> position;

Set a bit value to a specific position

The steps we will follow to set a bit to a specific position,

  1. Set zero to the position in the number using AND operator with the bitmask complement
  2. And then set the desired bit value to the position using OR operator

Let’s say our number is 0b100100, and we will set bit 0 at position 2 from the right.

 0b100101
      ^ 2nd position to set 1

Generating mask,

int bitMask = 1 << 2; // This will generate the number 0b000100
int bitMaskCompliment = ~bitMask; // This will generate number 0b...111011

Setting zero to the specific position of the number,

  0b100101
& 0b111011
  ________
  0b100001

And then, we can just use the OR operator to set the desired bit value.

  0b100001
| 0b000000 // We can get it by: bitValue<<2
  ________
  0b100001

Sample code,

int position = 2;
int bit = 0;
int number = 0b100101;

int bitMask = 1 << position;
int bitMaskCompliment = ~bitMask;

int numberWith0AtThePosition = number & bitMaskCompliment;

int result = numberWith0AtThePosition | bit << position;