Software question about U8x8 library

Projects Programming
1

It uses an expression (&u8x8) in its code. Searching has not told me what this express expands to or means. I would appreciate someone clarifying this for me.

Thank you,

Joe

2

"address of variable u8x8" probably (the address of the first character in) an array of characters.

3

How much do you know about pointers ?
Is there a variable named u8x8 declared in the sketch ?

Please post the full sketch that contains the expression that you are asking about, using code tags when you do

4

U8X8 Library.

5

So, the ampersand stands for 'address'? as in a pointer?

6

Yes - "address of" the first element of the array. (Also called "pointer to" the first element, but I believe that is not always correct)

Take an hour (or many) to look at pointers, linked lists and structures. These will be essential as your programs increase in complexity.

7

Thank you, I know about pointers (class about 40 yrs ago) just didn't know what the ampersand meant when not use as an and operator. I was digging through a program and it's libraries trying to find when the SW bit bang got the 0x3C or 0x78 address to send when I came upon this. I know the program did it since I saw the address being sent by a logic analyzer, but was trying to find in the code where it happened. This program: GitHub - avaldebe/TinyI2CScanner: Micro I2C-Scanner with 0.96" Oled and ATtiny85

8

what does the * mean? ei: 'const uint8_t *font;" is it also a pointer? or something else?

9

The asterisk says "a pointer to a constant uint8_t named font"
The asterisk is also called the "dereference" operator.

I found examples of a variable, address and pointer/deref:

int myAge = 43;     // An int variable
int* ptr = &myAge;  // A pointer variable, with the name ptr, that stores the address of myAge

// Output the value of myAge (43)
printf("%d\n", myAge);

// Output the memory address of myAge (0x7ffe5367e044)
printf("%p\n", &myAge);

// Output the memory address of myAge with the pointer (0x7ffe5367e044)
printf("%p\n", ptr);
10

In the U8g2 library, the only file that seems to set the i2c address is src/clib/u8x8_cad.c and the address is in the form 0x078 with the extra leading zero for some reason.

11

Thank you, found the Arduino language reference. Don't know why I didn't think of that before.
Also finally dragged out my old C Course book and reviewed pointers. Boy my 80 yr old brain gets boggled with that.

David: Thank you. Did a grep on the files for 0x3c or 0x78 and didn't find it because it is 0x078.