copy multidimensional array C - c

Question

I'm new to C and I created some code that doesn't work...
I get a warning while initLetterLib(): integer conversion resulted in truncation
I try to memcpy my libraryLetter into my outputLED, but it doesn't work.
I just get 0x00 into my outputLED.
I tried to copy something else in outputLED - this worked really fine.
But I dont get why there is a problem with my libraryLetters...
#define LETTER_WIDTH 6
typedef unsigned char letter[LETTER_WIDTH];
letter libraryLetters[128];
void initLetterLib(){
*libraryLetters[0x20] = 0x000000000000; // Blank
*libraryLetters['A'] = 0xFE909090FE00;
*libraryLetters['H'] = 0xFE101010FE00;
*libraryLetters['L'] = 0xFE0202020200;
*libraryLetters['O'] = 0xFE828282FE00;
*libraryLetters['U'] = 0xFE020202FE00;
*libraryLetters['R'] = 0xFE9894946200;
*libraryLetters['Z'] = 0x868A92A2C200;
*libraryLetters['I'] = 0x0000FE000000;
*libraryLetters['F'] = 0xFE9090808000;
}
// takes a String and generates the outputsequence for LEDs
unsigned char * stringToLEDText(char* textString)
{
static unsigned char outputLED[LED_STEPS];
unsigned char i = 0; // index
// check length of string text
unsigned short length = strlen(textString);
// if more than 10 letters are used return error
if (length > LETTERS_LED_OUTPUT)
{
printf("Error: Too much letters. Just 10 Letters are allowed\n");
return 0;
}
// through complete string
for (i = 0; i < length; i++)
{
memcpy(&outputLED[i * LETTER_WIDTH], &(libraryLetters[textString[i]]),
LETTER_WIDTH);
}
// fills rest with 0
for (i = length * LETTER_WIDTH; i < LED_STEPS; i++)
{
outputLED[i] = 0x00;
}
return outputLED;
}
Any ideas?
Thanks
Fabian

Answer 1

Your code doesn't make much sense. First of all, hiding an array behind a typedef is not a good idea. Get rid of that.
Using the default "primitive data types" of C is not a good idea either, since these are non-portable and of varied length. Instead use the stdint.h types. This is pretty much mandatory practice in embedded systems programming.
As for the actual problem, you can't assign an array like this
*libraryLetters[0x20] = 0x000000000000;
This doesn't make any sense. You are telling the compiler to store a 64 bit integer in the first byte of your 6 byte array. What you probably meant to do is this:
const uint8_t letters [128][LETTER_WIDTH] =
{
[0x20] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
['A'] = {0xFE, 0x90, 0x90, 0x90, 0xFE, 0x00};
...
};
Assuming this is a symbol table for some display. If so it should be const and allocated in flash.

Answer 2

*libraryLetters[x] is of type unsigned char and you are trying to assign a number to it outside the range of an unsigned char.
It looks like you are trying to assign a sequence of 6 bytes to *libraryLetters[x]. One way to do that is using memcpy, for example:
memcpy(libraryLetters['A'], "\xFE\x90\x90\x90\xFE\x00", 6);

Answer 3

You define your letter type as unsigned char which will only hold a single byte, but then you attempt to store a 6 byte integer. So you only get the last byte, which is zero in all your letters, if you want to be able to use an arbitrary length of the letter array. Otherwise, it will be much easier to use a 64-byte type, as suggested in the comments.
Instead, you should add the letters as
libraryLetters['H'][0] = 0xFE;
libraryLetters['H'][1] = 0x90;
...
Or you could use memcpy(libraryLetters['A'], letter_number, LETTER_WIDTH) as suggested by Ian Abbott.