>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 var

>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