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Comment by uecker

18 hours ago

Right. Also it might it sound like array-to-pointer decay is forced onto the programmer. Instead, you can take the address of an array just fine without letting it decay. The type then preserves the length.

6 comments

uecker

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WalterBright  14 hours ago

C: int foo(int a[]) { return a[5]; }

    int main() {
        int a[3];
        return foo(a);
    }

    > gcc test.c
    > ./a.out

Oops.

D: int foo(int[] a) { return a[5]; }

    int main() {
        int[3] a;
        return foo(a);
    }

    > ./cc array.d
    > ./array
    core.exception.ArrayIndexError@array.d(1): index [5] is out of bounds for array of length 3

Ah, Nirvana!

How to fix it for C:

https://www.digitalmars.com/articles/C-biggest-mistake.html

  • uecker  6 hours ago

    You need to take the address of the array instead of letting it decay and then size is encoded in the type:

      int foo(int (*a)[6]) { return a[5]; }
  int main() {
  int a[3];
    return foo(&a);
  }

    Or for run-time length:

      int foo(int n, int (*a)[n]) { return (\*a)[5]; }
  int main() {
    int a[3];
    return foo(ARRAY_SIZE(a), &a);
  }
  /app/example.c:4:38: runtime error: index 5 out of bounds for 
 type 'int[n]'

    https://godbolt.org/z/dxx7TsKbK\*