Question

In Cython glue declarations, how do I represent a C struct type containing an anonymous union? For example, if I have a C header file mystruct.h containing

struct mystruct
{
    union {
        double da;
        uint64_t ia;
    };
};

then, in the corresponding .pyd file

cdef extern from "mystruct.h":
    struct mystruct:
        # what goes here???

I tried this:

cdef extern from "mystruct.h":
    struct mystruct:
        union {double da; uint64_t ia;};

but that only gave me “Syntax error in C variable declaration” on the union line.

Answer 1

You can’t nest declarations to the best of my knowledge, and Cython doesn’t support anonymous unions AFAIK.

Try the following:

cdef union mystruct_union:
    double lower_d
    uint64_t lower

cdef struct mystruct:
    mystruct_union un

Now access the union members as un.lower_d and un.lower.