Question

I have some code I have in the Arduino environment that requires x (in increments of 8) boolean values that are manipulatable during run time for some shift register code. So currently I am using a boolean array like so:

 #define number_of_shiftRegisters 220 //num of 8 bit shift registers

 #define numOfRegisterPins number_of_shiftRegisters * 8 //number of booleans needed

 boolean registers[numOfRegisterPins]; //boolean array

But I was running out of RAM around 200 (1600 booleans) and didn’t know why until I saw that, even though booleans are 1 bit, they are stored in 8 bits of data.

As I said before, the number of bools needed is always in an increment of 8, so I don’t know if that could work to my advantage.

Is there a more memory efficient way to store 1000+ boolean values and still be able to reference them by index?

Or… At least more memory efficient that will not cost significantly more CPU time to set and iterate through?

I had thought about a char array, and then bit masking each char to access the individual bits. But I didn’t know if there was an easier way, or if this would take up considerably more CPU time.

Answer 1

Yes, you could easily use masking to get around that issue..

Every byte (unsigned char) will contain 8 boolean values, to get the i-th you can just use values & (1 << i) in if tests, and it will work since if the correct bit is set, then result will be != to 0.

To set instead a bit just shift it and or to the value: values | (1 << i) (in case of unset you have to AND it with 0).

Another solution could be to use a packed struct:

struct Bools
{
  int b1 : 1;
  int b2 : 1;
  int b3 : 1;
  ... // up to b8
}

This should manage elements with direct access to the boolean value and allow you to define an union to manage them either as 8 single bit booleans value either as bytes.