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Comment by trevcanhuman | Hacker News Reader

Using the post increment operator for pointer operations ? Would have never imagined that. I've only seen it used in for loops for no reason at all, really.

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It's common enough, like in a typical memcpy implementation:

    while(size--)
       *dst++ = *src++;

Or chaining it even further for copying a null-terminated string. The assignment operator returns the same value that was just stored, so it can be used as the conditional on a while loop.

    while(*dst++ = *src++);

Incredibly succinct, ridiculous powerful, and way too easy to overrun array bounds.

Yep, if there is no #$00 ('\0') at the end of the string, an exploit will ensue, especially if the attacker manages to modify the string first.

It's one place C shows its roots ....

mov (r0)+, (r1)+ is a PDP11 instruction

as is mov -(PC), -(PC)

...Or

  move.l (a0)+, (a1)+

I think those are 68k ops - PDPlls didn't have special addressing registers (just general R0-R7) and MOV/MOVB opcodes

Of course they are MC68000 family assembler instructions, but the principle is exactly the same.

And yet it's from B which was not designed for a machine with auto increment.

It's very common, like ABC of pointer arithmetic. Especially if one has coded in assembler first, then took up C, it's the most natural thing to do.

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