The following project contains two Proof of Concepts of interop errors that occur whenever Swift code tries to gain access to C arrays declared in C or C++ code.
The first issue is a PoC of an interop error that occurs whenever Swift code tries to access an extern C array.
Another issue is that a Flexible Array Member (FAM) of a struct cannot be accessed from Swift. The field is thereby reported as missing by the Swift Compiler.
A FAM is a c99 feature allowing an incomplete array declaration in C (and some non-standard C++ implementations), or an array declaration with no specified size in the last position of a struct.
Generally speaking, FAMs are used to support variable length arrays in structs (or in C++'s case, also classes), or those whose length is unknown at compile time or whose implementations' length may vary (even if known at compile time for each separate implementation).
For both issues, if the C code is modifiable, a workaround is to access a pointer to the C array or have a function retrieve or set a particular value.