3 ms·

This is what I was going for in the blog post, but I got confused after seeing these comments as Clang _does_ compile this when the buffer is of static storage

by lochsh 7y ago

This is what I was going for in the blog post, but I got confused after seeing these comments as Clang _does_ compile this when the buffer is of static storage class. Which I don't think is standard -- but it's not using VLAs. I wondered if it just has constant expression semantics for const variables. Weirdly, adding a _Static_assert to test this theory proves it for c99 but not c11 :/ https://godbolt.org/z/q-bb-n https://godbolt.org/z/q-bb-n c99 with clang https://godbolt.org/z/ad14Ah https://godbolt.org/z/ad14Ah c11 with clang https://godbolt.org/z/xJSDQa https://godbolt.org/z/xJSDQa c11 with gcc (which is the only one giving the output I'd expect)

eMSF 7y ago
>I wondered if it just has constant expression semantics for const variables. That would be my guess also, for applicable const variables. File scope const variables are quite constexpr-y in C anyway, since C requires all file scope variable initializers to be constant expressions (C++ only requires that for constexpr variables). Toying around with clang in Godbolt, it seems that there are some quirks regarding this. The following is accepted: static const int n = 0; int buf[n]; // invalid zero-length array is accepted // probably another non-standard extension But the following is not, despite n having the same zero value: static const int n; int buf[n]; // complains about a file scope VLA
_kst_ 7y ago
The C standard permits implementations to support additional forms of constant expressions. Try "clang -std=c11 -pedantic-errors".