https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100124
Bug ID: 100124
Summary: Why is "flexible array member '...' in an otherwise
empty '...'" an issue?
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc at behdad dot org
Target Milestone: ---
Hi,
In HarfBuzz we extensively use the Struct Hack [0]. Up until now we've used
"array[1]" for that. This upsets ubsan [1]. So I'm looking to replace it with
flexible arrays on compilers that support it.
However, trying to do that I get error if the flexible-array is the only
member. Clang has no issues with it, but gcc gives me: "flexible array member
'...' in an otherwise empty '...'".
```
struct UnsignedArray {
int array[];
};
```
I've seen:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69550
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71742
which suggests that disallowing flexible arrays in structs that have no other
named member is intentional. But I cannot find the reason. Can someone please
help me understand, and suggest a solution here?
Note that if I use `int array[0]` instead, then gcc warns everytime in code we
access that array with a constexpr value, like `array[0]` when we know it's
safe to do. That is, gcc seems to treat `int array[0]` literally, not as a
flexible array.
Thank you.
[0] http://c-faq.com/struct/structhack.html
[1] https://github.com/harfbuzz/harfbuzz/issues/2953
