How to check how a bit is set in c?

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How to check a bit in a variable whether it is set or not using C language

Posted 3-Jan-13 23:56pm

steven8Gerrard

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3 solutions

Solution 3

The solutions listed above are good for unstructured testing. If you are designing a system from scratch and you know that the data structure for your algorithm is going to need to check bits then you should investigate the use of bit fields.

http://en.wikipedia.org/wiki/Bit_field[^]

Posted 4-Jan-13 3:48am

Andy Bantly64K

v2

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BobJanova · Accepted Answer · 2013-01-04T00:27:00

Solution 2

Related to CP's answer:

#define bit_set(val, bit_no) (((val) >> (bit_no)) & 1)

This numbers bits from (n-1) to 0 from the high value bits to the low, i.e. in a short the lowest bit (value 1) is bit number 0, and the highest (value 32768) is number 15.

Posted 4-Jan-13 0:27am

BobJanova

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steven8Gerrard 4-Jan-13 6:53am

Thank you . Much appreciated

CPallini · Accepted Answer · 2013-01-04T00:04:00

Solution 1

(For instance) With a shift and a bitwise and, e.g.

C

// check if bit 5 is set
if ( (val >> 5) & 1)
{
  // bit is set
}
else
{
  // bit unset
}

Posted 4-Jan-13 0:04am

CPallini

Updated 4-Jan-13 0:10am

v2

Comments

steven8Gerrard 4-Jan-13 6:53am

Thank you . Much appreciated

CPallini 4-Jan-13 6:57am

You are welcome.