Bitwise Operators in ANSI C

The basic bitwise operations are NOT, AND, OR and XOR.

Let us consider two 8 bit numbers a and b where a = 36 and b = 6.

	2^7	2^6	2^5	2^4	2^3	2^2	2^1	2^0
	128	64	32	16	8	4	2	1
36	0	0	1	0	0	1	0	0
6	0	0	0	0	0	1	1	0

The best way for working with bits and bytes is by using the stdint.h ANSI library. This library helps you by making your code more portable (some compilers have 16 bit integers and 32 bit long integers, while others have 32 bit integers and 64 bit long integers)

Binary decomposition example

stdint.h provides 8, 16, 32 and 64 bit compiler-independent primitive data types both signed and unsigned.

In the examples below, I will use unsigned 8 bit integers, which shall translate to the uint8_t type.

To include the library when using C:

#include<stdint.h>

1.NOT operation

Description
Basically, negating a number means that every 0 becomes and every 1 becomes 0.

a	0	0	1	0	0	1	0	0	36
~a	1	1	0	1	1	0	1	1	219
b	0	0	0	0	0	1	1	0	6
~b	1	1	1	1	1	0	0	1	249

Syntax

#include<stdio.h>
#include<stdint.h>

int main(void)
{
   uint8_t a = 36;
   uint8_t b = 6;
   uint8_t nota = ~a;
   uint8_t notb = ~b;
   printf("~a %u\n",nota);
   printf("~b %u\n",notb);
   return 0;
}
/*Output
~a 219
~b 249
*/

2.AND operation

Description
The bitwise AND operation compares the bits on every position and if both bits are 1, the result bit will be 1. Otherwise, the result bit will be 0.

a	0	0	1	0	0	1	0	0	36
b	0	0	0	0	0	1	1	0	6
a AND b	0	0	0	0	0	1	0	0	4

Syntax

#include<stdio.h>
#include<stdint.h>

int main(void)
{
   uint8_t a = 36;
   uint8_t b = 6;
   uint8_t aandb = a&b;
   printf("a&b %u\n",aandb);
   return 0;
}
/*Output
a&b 4
*/ 

3.OR operation

Description
The bitwise OR operation compares the bits on every position and if one of the bits is 1, the result will be 1. Otherwise (if both bits are 0), the result will be 0.

a	0	0	1	0	0	1	0	0	36
b	0	0	0	0	0	1	1	0	6
a OR b	0	0	1	0	0	1	1	0	38

Syntax

#include<stdio.h>
#include<stdint.h>

int main(void)
{
   uint8_t a = 36;
   uint8_t b = 6;
   uint8_t aorb = a|b;
   printf("a|b %u",aorb);
   return 0;
}
/*Output
a|b 38
*/

4.XOR operation

Description
The bitwise XOR operation compares the bits on every position and if one of the bits is 1 and the other is 0 the result will be 1. Otherwise (if both bits are 1 or 0) the result will be 0.

a	0	0	1	0	0	1	0	0	36
b	0	0	0	0	0	1	1	0	6
a XOR b	0	0	1	0	0	0	1	0	34

Syntax

#include<stdio.h>
#include<stdint.h>

int main(void)
{
   uint8_t a = 36;
   uint8_t b = 6;
   uint8_t axorb = a^b;
   printf("a^b %u",axorb);
   return 0;
}
/*Output
a^b 34
*/

Below you can see the logic table for the AND, OR and XOR operations:

a	b	AND	OR	XOR
0	0	0	0	0
0	1	0	1	1
1	0	0	1	1
1	1	1	1	0

Question: In which context do you use bitwise operations?

References:
http://en.wikipedia.org/wiki/Bitwise_operations_in_C