// MEMORY · WHAT'S UNDERNEATH //

A pointer is just an address you stored somewhere

Pointers are where a lot of people quietly decide programming isn't for them. The asterisks, the arrows, *p versus &p. The 6502 strips all of it away, because here a pointer isn't a type or a concept — it's two bytes in memory holding an address, and one addressing mode that goes and reads it.

Store an address like any other number

Put the address $C000 into two bytes of zero page — low byte, then high byte, the 6502’s usual order. Those two bytes are now a pointer. Not “like” a pointer — they hold an address, which is the entire definition.

6502 · A POINTER IN ZERO PAGE

        lda #$00
      sta $10        ; $10 = low byte  of $C000
      lda #$c0
      sta $11        ; $11 = high byte of $C000
                     ; the pair $10/$11 now "points to" $C000

Setting a pointer is just writing an address into memory. p = &thing, with the curtain up.

Dereferencing is one addressing mode

To follow the pointer — to read the byte it points at — you use indirect indexed addressing: lda ($10),y. The CPU reads the address out of $10/$11, adds Y, and fetches from there. That little ( ) is the asterisk in *p:

6502 · WALKING A STRING THROUGH A POINTER

        ldy #0
loop:   lda ($10),y    ; A = *(p + y)  — dereference
      beq done       ; zero byte ends the string
      jsr print
      iny            ; y++  — walk one byte along
      bne loop
done:   rts

Increment Y and you're doing pointer arithmetic. Change $10/$11 and the same loop walks a different array.

Every pointer idea is now standing in the open. A null pointer is the pair holding $0000 — dereference it and you read address zero, garbage, no guard rail. A dangling pointer is two bytes still holding an address whose data you’ve since reused. A pointer to a pointer is a pointer whose target happens to be another two-byte address. None of it is abstract here — it’s just which bytes hold which addresses.

The asterisk was never the hard part — it was the abstraction hiding the bytes. Once you’ve set a pointer with two stas and followed it with one lda ($10),y, the C melts. A pointer is an address you stored somewhere. That’s the whole secret.

>Every great programmer started with one instruction.