C array types are weird

(anselmschueler.com)

49 points | by signa11 1 day ago

6 comments

  • kazinator 34 minutes ago
    There is a history to it; in one of the predecessor languages, like B, Ritchie actually had arrays that had a hidden pointer to their start. The "array to pointer decay" was actually a real operation that loaded an address from memory, and it was possible to twiddle the bits to relocate an array. One problem with it was no way to initialize such a pointer field that would allow an array to live in dynamically allocated storage (no constructors in the language).

    So in short, the bad design (array values produce pointers) was informed by conceptual compability with an earlier design in which that was literally happening.

  • uecker 1 day ago
    In practice, the [static n] notation can give you useful warnings and bounds checking.

    https://godbolt.org/z/PzcjW4zKK

    And while the (*array_ptr)[3] notation take a moment to get used to, it is very logical. If you have a pointer to an array, you dereference it first and then indx into it. Again, useful for bounds checking: https://godbolt.org/z/ao1so9KP7

    • keyle 1 hour ago
      I know of this notations but I don't see many people using [static n].

      Not sure why, maybe it doesn't feel like C anymore, maybe it feels hacky?

      typically if you're passed an array you'd want to get more anyway, so you'd get passed a struct. Not sure.

    • dnautics 2 hours ago
      What is **int[3][5]
      • thrance 1 hour ago
        A pointer to a pointer to a pointer to a pointer of integers.
      • ori_b 2 hours ago
        A syntax error. You need a variable name, not a type name, in the middle.
        • fusslo 1 hour ago
          or a rejected PR
        • ori_b 1 hour ago
          And if you want 'int **arr[a][b]', it's a value that when you say 'x = **arr[m][n]', will evaluate to an int and assign it to x. Postfix has higher precedence than prefix.
  • the__alchemist 2 hours ago
    This is one of the things that I feel is an inappropriate abstraction that is around for historical reasons. When I do FFI to call C from rust, I usually wrap the generated API (Which is pointer based) into rust's &[] array syntax. Arrays/lists/Vecs etc in most non-C languages feel like an abstraction over a collection of items; I feel like C's exposing the pointer directly is taking a low-level memory/MMIO operation and inserting it into business logic. Conceptually, I like to keep them separate; pointers for writing drivers, accessing registers, writing to flash memory etc. Arrays/lists/vecs for higher level operations on collections.

    Tangent: I have a pet theory that part of Zig's raison d'etre is to fix some of the problems with C, while accommodating its pointer-based data structures, and the resulting patterns.

  • fatty_patty89 2 hours ago
    there's no array type in c
    • colejohnson66 2 hours ago
      Yes it does. It just decays to a pointer at the slightest touch.
      • throwaway27448 1 hour ago
        So why are we discussing it
        • dwattttt 1 hour ago
          Because doing a dance to avoid it decaying conveys better information to both the compiler and downstream users of your code.
  • IncreasePosts 2 hours ago
    Paging walter bright
    • glouwbug 2 hours ago
      C's biggest mistake.

      But in other news most don't know that a[3] == 3[a]

  • throwaway27448 1 hour ago
    Why are we still discussing c in 2026? Why are you intentionally hamstringing yourself unless you're using fucking hp-ux
    • smackeyacky 55 minutes ago
      Embedded programming is still in C for a lot of micro controllers and whatnot. If you’re programming with limited resources it’s essential to understand pointers and arrays. Likely you won’t be doing anything useful without them
    • cartoonfoxes 1 hour ago
      • pdpi 25 minutes ago
        As always, the TIOBE Index is of dubious value. The fact that it ranks Delphi above both Go and Rust should give you an idea of why.
      • mianos 1 hour ago
        p.s. in case you don't want to follow the link, number 2 on the list