C - Get a bit from a byte

Question

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how to get bit by bit data from a integer value in c?

I have a 8-bit byte and I want to get a bit from this byte, like getByte(0b01001100, 3) = 1

Arrgh, so many duplicates! Let me find one... – Oliver Charlesworth Jan 01 '12 at 22:19 — Oliver Charlesworth, Jan 01 '12 at 22:19

ouah · Accepted Answer · 2012-01-01T22:32:26.090

27

Firstoff, 0b prefix is not C but a GCC extension of C. To get the value of the bit 3 of an uint8_t a, you can use this expression:

((a >> 3)  & 0x01)

which would be evaluated to 1 if bit 3 is set and 0 if bit 3 is not set.

edited Jan 01 '12 at 22:32

answered Jan 01 '12 at 22:23

ouah

4

Just helping those who may be less familiar with binary, bit 3 is actually the fourth digit from the right, i.e., 1**1**110 If you wanted to get the third digit from the right, you would right shift 2, the fifth, 4, etc. – tobahhh Mar 01 '18 at 00:27

score 6 · Answer 2 · answered Jan 01 '12 at 22:18

6

First of all C 0b01... doesn't have binary constants, try using hexadecimal ones. Second:

uint8_t byte;
printf("%d\n", byte & (1 << 2);

answered Jan 01 '12 at 22:18

cnicutar

score 1 · Answer 3 · answered Jan 01 '12 at 22:19

1

Use the & operator to mask to the bit you want and then shift it using >> as you like.

answered Jan 01 '12 at 22:19

Francis Upton IV

3 Answers3