OK, this looks like a CFFI bug.
If I use malloc/free/memset manually it works fine.
Code:
from cffi import FFI
ffi = FFI()
ffi.cdef("""
typedef struct PROPVARIANT {
unsigned short vt;
unsigned short wReserved1;
unsigned short wReserved2;
unsigned short wReserved3;
union {
int intVal;
wchar_t* bstrVal;
/* shortened for clarity */
};
} PROPVARIANT;
typedef unsigned long long HRESULT;
typedef uint32_t PROPID;
HRESULT GetNumberOfFormats(uint32_t * numFormats);
HRESULT GetHandlerProperty2(uint32_t index, PROPID propID, PROPVARIANT * value);
void * malloc(size_t);
void memset(void*, int, int);
void free(void*);
""")
S_OK = 0x00000000 # Operation successful
VT_BSTR = 8
kExtension = 2
dll7z = ffi.dlopen('7z.dll')
C = ffi.dlopen(None)
num_formats = ffi.new('uint32_t*')
assert dll7z.GetNumberOfFormats(num_formats) == S_OK
print(num_formats[0])
tmp_pvar = ffi.cast("PROPVARIANT*", C.malloc(ffi.sizeof('PROPVARIANT')))
C.memset(tmp_pvar, 0, ffi.sizeof('PROPVARIANT'))
for i in range(num_formats[0]):
assert dll7z.GetHandlerProperty2(i, kExtension, tmp_pvar) == S_OK
assert tmp_pvar != ffi.NULL
assert tmp_pvar[0].vt == VT_BSTR
print(ffi.string(tmp_pvar[0].bstrVal))
C.free(tmp_pvar)