I am coding in C programming. Let's say I have a character: char letter=0x0000; So the binary data for the letter is now "00000000" let say I want change the binary data to "10000000" and later to change it "10010000", is there a bitwise operator or method that would allow me to change a "0" to a "1" or "1" to a "0" at a specific position. Also is this possible?
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1Yes it is possible, there are bitwise operators in C.wildplasser– wildplasser2013-10-26 18:22:31 +00:00Commented Oct 26, 2013 at 18:22
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Can you show me the bitwise operator that would be used to go from "00000000" to "00100000" (change "0" at position 2 to "1")?user2106253– user21062532013-10-26 18:25:47 +00:00Commented Oct 26, 2013 at 18:25
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bit.ly/1andHfTCharlie Burns– Charlie Burns2013-10-26 18:27:08 +00:00Commented Oct 26, 2013 at 18:27
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Check the ans. by templatetypedefArpit– Arpit2013-10-26 18:27:52 +00:00Commented Oct 26, 2013 at 18:27
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That is not position 2. Bits are usually counted from right to left, starting with zero, so it would be bit 5.wildplasser– wildplasser2013-10-26 18:28:08 +00:00Commented Oct 26, 2013 at 18:28
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3 Answers
If you XOR any bit with a 1 bit, it toggles its value:
0 ^ 1 = 1
1 ^ 1 = 0
Similarly, if you XOR any bit with 0, it keeps the same value:
0 ^ 0 = 0
1 ^ 0 = 1
Therefore, you can flip the nth bit of a number by XORing it with a number that has zero bits everywhere except in bit n:
val ^= (1 << n);
Hope this helps!
answered Oct 26, 2013 at 18:25
templatetypedef
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5 Comments
templatetypedef
@wildplasser- I'm not sure I understand your comment... can you clarify?
Leeor
@JackGabishya, Keep in mind that XOR with some bitmask toggles the bit values where the mask has ones, an OR with the same mask would always turn then to 1, and an AND with an inverted mask would always turn them to 0.
templatetypedef
@Leeor- Since the question specifically mentions switching 0 to 1 or 1 to 0, I assumed that the OP wanted to toggle the bits. But you're right - this might not be exactly what they want.
Michael Rawson
Your first example has a typo:
1 ^ 1 is 0, not 1.templatetypedef
@MichaelRawson- Oh whoops! Thanks for spotting that. Fixed!
Yes it is very much possible. Just use bitwise exclusive OR or simply XOR operator on the number with 2 to the power of n where as n is the digit you want to change. ^ is the XOR operator in C.
000000 (decimal 0)
^ 100000 (decimal 32 = 2 power 5 = 1 << 5)
= 100000
1010 (decimal 10)
XOR 0010 (decimal 2 = 2 power 1 = 1 << 1)
= 1000
You can calculate 2 to the power of n by simply shifting bits in 1 by n bits. So 2 to the power of 4 can be obtained by shifting bits in 1 by 4 places.
inputNum ^ (1 << n) will give what you needed if toggling is all you need.
Bitwise XOR "^"
bit a bit b a ^ b (a XOR b)
0 0 0
0 1 1
1 0 1
1 1 0
However remember that doing XOR on a bit that already has 1 will convert it to zero. because 1 ^ 1 = 0;
If you just want to convert 0 to 1 and keep 1 if it is already there. You can have to use bitwise Or operator.
Bitwise OR "|"
bit a bit b a | b (a OR b)
0 0 0
0 1 1
1 0 1
1 1 1
Following is an example
11001110
| 10011000
= 11011110
Source: http://en.wikipedia.org/wiki/Bitwise_operations_in_C & http://en.wikipedia.org/wiki/Bitwise_operation
Comments
You can use bitwise AND (&) and OR (|) operator. For example:
01001000 | 10111000 = 11111000
This is done following: 72 | 184 = 248
(72 = 64+8)
For details see following tutorial: http://www.cprogramming.com/tutorial/bitwise_operators.html
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