How to set/reset multiple bits in C

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I know that in order to set a bit we use num|(1<<n), where it sets the (n+1)th bit. How can I set/reset more than 1 bit at a time?

Posted 14-Jul-14 6:08am

Jeevan83

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Solution 2

Quote:
num|(1<<n)

Actually you use

C

num |= (1 << n);

to set the bit n of num (for instance num |= (1 << 0); sets the bit 0).

To set (clear) multiple bits you have just to OR (AND) the num with the appropriate constant.

For instance

C

num |= 0xFF;

sets the bits 0..7 of num

while

C

num &= ~0xFF;

clears the same bits.

Posted 14-Jul-14 8:21am

CPallini

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-07-14T06:21:00

You need to OR those bits together: http://en.wikipedia.org/wiki/Operators_in_C_and_C++#Bitwise_operators[^].

For example 1 | (1<<1) | (1<<3) gives you 11 (zero, first and third bits a are set, other bits are clear). You can also OR ('|', '|=')any bit set to previously assigned value:

C++

existingBitSet |= bitsToSet;

For clearing bits, first OR them together (obtain bitsToClear, see below) and than use the operators '& ('&=') and ~ (not):

C++

existingBitSet &= ~bitsToClear;

See also: http://en.wikipedia.org/wiki/Bit_manipulation[^].

—SA