bool array vs bit array in C

Question

I am in need of implementing an efficient bit array in C. From what I have seen C does not support this so you can use an array of integers (according to one site I looked at) and then use a shift to access individual bits. Would simply declaring a bool array be the same thing or is this less memory efficient?

A _bool in C is generally an int internally. A _bool[] uses about 32 times (give or take) as much memory as the array of integers with bit-shifted access. — user3185968
– user3185968, Commented Nov 17, 2014 at 22:42
If using C++ is a viable option for you, std::vector<bool> offers the bit-packing space optimization you're describing. — Jim Lewis
– Jim Lewis, Commented Nov 17, 2014 at 22:48
@EOF: _Bool (not _bool) is typically 1 byte, not the same size as int. — Keith Thompson
– Keith Thompson, Commented Nov 17, 2014 at 22:48
@KeithThompson: Yeah, you're right. So it's just a factor of CHAR_BIT. I said give or take. You've just taken a lot... — user3185968
– user3185968, Commented Nov 17, 2014 at 22:49

Carl Norum · Accepted Answer · 2014-11-17 22:46:26Z

6

Yes, a simple _Bool array require more storage than an array of integers combined with some bit-shifting. The _Bool array stores one bit of data in a sizeof(_Bool) space (normally a single byte). The integer array can store many more bits per byte (minimum 8).

answered Nov 17, 2014 at 22:46

Carl Norum

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