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Re: C arrays as __block variables
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Re: C arrays as __block variables


  • Subject: Re: C arrays as __block variables
  • From: Bill Bumgarner <email@hidden>
  • Date: Sat, 26 Jun 2010 19:16:33 -0700

On Jun 26, 2010, at 6:38 PM, Matt Neuburg wrote:

> The docs say: "There are two further restrictions on __block variables: they
> cannot be variable length arrays, and cannot be structures that contain C99
> variable-length arrays."
>
> This would seem to imply that a __block variable *can* be a *fixed* length
> array. But when I try to write into such an array inside a block, I get a
> compile error, "cannot access __block variable of array type inside block."
>
> Who's mistaken, the compiler or the docs? Thx - m.

Neither.   The issue is that a block array in C is, technically, sorta-kinda variable length unless you do something to make it fixed length. I don't remember the exact details beyond that it is a subtle edge case.

That something is typically to encapsulate it into a Struct.

This:

void foo() {
    char barfy[100];

    ^() {
        char b = barfy[0]; <<<< error: cannot access copied-in variable of array type inside block
        b = b;
    };
}

This compiles just fine:

void bar() {
    struct angus {
        char barfy[100];
    } kangus;

    ^() {
        char b = kangus.barfy[0];
        b = b;
    };
}

b.bum






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