Initialize and read from a PROGMEM array of pointers to PROGMEM arrays

Question

I'm working on a project for the arduino uno for which I need multiple constant arrays of bytes. Such an array is initialized like so:

const byte charR[] PROGMEM = {
 B01111111,//top half
 B01111111,
 B01000100,
 B01000110,
 B01101111,
 B00111001,
 B00000000,
 B01111000,//bottom half
 B01111000,
 B00000000,
 B00000000,
 B01111000,
 B01111000,
 B00000000
};

This array represents the capital letter R. I read the nth byte of this array like so:

nth_byte = pgm_read_word(charR+n);

This is all fine and good so far, but now I need to take it a step further. I need to create the array message[]. I need to use message[] to read byte arrays in a certain sequence. For instance:

message[] = {
 charR,
 chare,
 charp,
 charl,
 chary,
 charspace,
 charp,
 charl,
 chare,
 chara,
 chars,
 chare
};

Each entry in message[] refers to a byte array that represents a character. Notice how multiples appear. This is kind of like a 2-D array, but I want to save progmem by only defining each character once.

How do I properly initialize message[]? Will I need to use pointers for this? How do I properly get the array size or yth byte of the xth entry in message[]?

Answer 1

const byte* const message[] PROGMEM =

to use an item, load it in RAM

strcpy_P(buffer, (byte*)pgm_read_word(&(message[i])));

source Arduino reference - PROGMEM

• Juraj: @bo-thompson, did it help?
• Bo Thompson: Sorry for the delay, I've been separated from the microcontroller running this project for the last week. Hopefully I will return to it in the coming week and I will mark this as an answer as soon as I've verified that I can understand and use it.