Setting and clearing bits in C

Question

I have some trouble with a C program that does some bit manipulation. In the program, I use an unsigned long long int variable to represent a 64 bit map, each bit representing a position on the map. I need to be able to update these bits (positions) i.e. setting or clearing a bit. To clear and set a bit, I do (0 is the least significant position):

map &= ~(1 << pos) // clear bit in position 'pos' map |= (1 << pos) // set bit in position 'pos'

The problem is that when i perform these operations, all the bits in the map which are to the left of pos get set to 0 (while I want only the bit in position pos to change).

What am I doing wrong?

This has been asked before, several times. The problem is the type of the 1. — user555045
– user555045, Commented Nov 14, 2015 at 17:30

Some programmer dude · Accepted Answer · 2015-11-14 17:30:41Z

The problem is that those shifts are done using the type int, which on all modern 64-bit systems are still 32 bits. You need to use the same type as map, i.e. unsigned long long:

1ull << pos

Note the ull which tells the compiler that the 1 is not an int but an unsigned long long.

Thank you very much. I knew it was something with the data types, but I didn't know how to make the shifts with the same type as the map.

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