Changing single bit in byte array

Question

So I have a byte-array representing the display attached to my Arduino:

byte theDisplay[8] = {
 B00000000,
 B00000000,
 B00000000,
 B00000000,
 B00000000,
 B00000000,
 B00000000,
 B00000000
};

Now I want to flip a single bit at an arbitrary position:

theDisplay[3][6] = 1;

This (probably) faulty method produces these errors:

In function 'void setup()':
sketch_sep14c:13:18: error: invalid types 'byte {aka unsigned char}[int]' for array subscript
 theDisplay[3][6] = 1;
 ^
exit status 1
invalid types 'byte {aka unsigned char}[int]' for array subscript

Is there an easy way to flip a single bit working with indexes like shown above?

• Juraj: arduino.cc/reference/en Bits and Bytes section
• gurkensaas: @Juraj I was aware of that, but I couldn't figure out how to set the 6th bit of the 3rd item in the array to 1.

Answer 1

The error occurs, because you try to use the syntax for a 2 dimensional array with a 1 dimensional array (since you have an array of bytes, not bits, and a microcontroller always works with at least one byte). For accessing the individual bits you need to use bitwise operators. For example this:

theDisplay[3] |= (1 << bitnumber); // for setting the bit
theDisplay[3] &= ~(1 << bitnumber); // for clearing the bit

with bitnumber being the number of the bit to change counted from least significant bit (in the binary representation in your code the rightmost digit) to most significant bit (the leftmost digit).

If you want to know, what exactly this does, you can google for bitwise operators in C++.

• Juraj: Arduino way is the bitSet function arduino.cc/reference/en/language/functions/bits-and-bytes/…
• gurkensaas: Thanks for your answer. Do I understand correctly that the top one sets the bit to 1 and the lower one sets the bit to 0?
• Edgar Bonet: There is also theDisplay[3] ^= (1 << bitnumber); for toggling the bit.
• Nick Gammon: @gurkensaas Yes, that is what "setting" and "clearing" means.