My question is rather simple, yet I cannot find an easy solution:
I have an integer greater or eqal 16, so at least 1000 in binary. I wish to flip the third bit using the bitwise NOT operator. In this case, it would be 1100.
Is there any operator which could do this? The ~-operator flips all bits as far as I know, not just one certain.
XOR with the bits that you want to flip.
int c = 0x10; // 10000b
int m = 0x08; // 01000b
c ^= m; // 11000b
Do
bit_fld ^= (1 << n)
where bit_fld is the bit field, and n=3 for third bit.
Now what you call 'flip' is actually called XOR. XOR in C(++) works like this:
int sixteen = 16; // 10000
int twentyfour = sixteen ^ 0x8; // flip the 4th bit. result: 24
int sixteen_again = twentyfour ^ 0x8; // again, flip the 4th bit. result: 16
On a side note: 16 in binary is 10000, not 1000.
check this site: http://www.daniweb.com/software-development/c/threads/41493 he has the same problem you have, and a couple of solutions!
void flipbit(unsigned* a, unsigned b)
{
*a ^= (1 << b);
}
#include <stdio.h>
int main(void)
{
int x = 0xFFFFFFFF;
int n = 0;
int y, i;
for (i=0 ; i < (int)sizeof(int)*8 ; i++) {
y = x ^ ~(1<<i);
printf("x=%x\ti=%d\ty=%x\n", x, i, y);
}
x = 0x0;
for (i=0 ; i < (int)sizeof(int)*8 ; i++) {
y = x ^ ~(1<<i);
printf("x=%x\ti=%d\ty=%x\n", x, i, y);
}
return 0;
}
/*
Output:
x=ffffffff i=0 y=1
x=ffffffff i=1 y=2
x=ffffffff i=2 y=4
x=ffffffff i=3 y=8
x=ffffffff i=4 y=10
x=ffffffff i=5 y=20
x=ffffffff i=6 y=40
x=ffffffff i=7 y=80
x=ffffffff i=8 y=100
x=ffffffff i=9 y=200
x=ffffffff i=10 y=400
x=ffffffff i=11 y=800
x=ffffffff i=12 y=1000
x=ffffffff i=13 y=2000
x=ffffffff i=14 y=4000
x=ffffffff i=15 y=8000
x=ffffffff i=16 y=10000
x=ffffffff i=17 y=20000
x=ffffffff i=18 y=40000
x=ffffffff i=19 y=80000
x=ffffffff i=20 y=100000
x=ffffffff i=21 y=200000
x=ffffffff i=22 y=400000
x=ffffffff i=23 y=800000
x=ffffffff i=24 y=1000000
x=ffffffff i=25 y=2000000
x=ffffffff i=26 y=4000000
x=ffffffff i=27 y=8000000
x=ffffffff i=28 y=10000000
x=ffffffff i=29 y=20000000
x=ffffffff i=30 y=40000000
x=ffffffff i=31 y=80000000
x=0 i=0 y=fffffffe
x=0 i=1 y=fffffffd
x=0 i=2 y=fffffffb
x=0 i=3 y=fffffff7
x=0 i=4 y=ffffffef
x=0 i=5 y=ffffffdf
x=0 i=6 y=ffffffbf
x=0 i=7 y=ffffff7f
x=0 i=8 y=fffffeff
x=0 i=9 y=fffffdff
x=0 i=10 y=fffffbff
x=0 i=11 y=fffff7ff
x=0 i=12 y=ffffefff
x=0 i=13 y=ffffdfff
x=0 i=14 y=ffffbfff
x=0 i=15 y=ffff7fff
x=0 i=16 y=fffeffff
x=0 i=17 y=fffdffff
x=0 i=18 y=fffbffff
x=0 i=19 y=fff7ffff
x=0 i=20 y=ffefffff
x=0 i=21 y=ffdfffff
x=0 i=22 y=ffbfffff
x=0 i=23 y=ff7fffff
x=0 i=24 y=feffffff
x=0 i=25 y=fdffffff
x=0 i=26 y=fbffffff
x=0 i=27 y=f7ffffff
x=0 i=28 y=efffffff
x=0 i=29 y=dfffffff
x=0 i=30 y=bfffffff
x=0 i=31 y=7fffffff
*/
I refer this link for bit operations in c.
