#35 Some structures with bitfields not properly handled by ctypes

[Marc Le Roy]

Hello,

I just found that some very simple packed C structures containing bitfields are not managed as expected by ctypes.

Attached file test5.c defines this structure:

typedef struct __attribute__ ((packed)) {
   unsigned int   F0:24;
   unsigned int   F3:24;
   unsigned int   F6:24;
   unsigned int   F9:24;
} StructF_T;

As expected, the memory layout seen by the C program is :
0x111111222222333333444444

Attached file test5.py defines this structure:

class StructF(ctypes.BigEndianStructure):
    _pack_ = 1
    _fields_ = [
        ('F0',      ctypes.c_uint, 24),
        ('F3',      ctypes.c_uint, 24),
        ('F6',      ctypes.c_uint, 24),
        ('F9',      ctypes.c_uint, 24),
    ]

The memory layout seen from Python is not consistent :
0x11111100222222003333330044444400
The layout is the same using ctypes.LittleEndianStructure.

Any idea ?
Marc

[Marc Le Roy]

The missing attachment :