python ctypes structure wrong byte size

Question

So I\'m trying to figure out why the size of my ctypes.Structure is not what it should be. My code is the following, theres also the calculation of what the siz

Answer 1

Ok so I've found the solution. Thanks to Andreas who told me that my problem has to do with the offset. So the solution is to add a _pack_ = 1 to the structure like that.

class FILE_HEAD(ctypes.Structure):
    _pack_ = 1
    _fields_ = [
        ("name", ctypes.c_char * 4),                    # 4 bytes
        ("size", ctypes.c_int),                         # 4 bytes
        ("Cal_l", ctypes.c_double),                     # 8 bytes
        ("Cal_r", ctypes.c_double),                     # 8 bytes
        ("Speed_ChL", ctypes.c_byte),                   # 1 byte
        ("Speed_Pulses_ChL", ctypes.c_int),             # 4 bytes
        ("Speed_factor_ChL", ctypes.c_double),          # 8 bytes
        ("Quantity_ChL", ctypes.c_char * 3),            # 3 bytes
        ("Description_ChL", ctypes.c_char * 32),        # 32 bytes
        ("Unit_ChL", ctypes.c_char * 8),                # 8 bytes
        ("Speed_ChR", ctypes.c_byte),                   # 1 byte
        ("Speed_Pulses_ChR", ctypes.c_int),             # 4 bytes
        ("Speed_factor_ChR", ctypes.c_double),          # 8 bytes
        ("Quantity_ChR", ctypes.c_char * 3),            # 3 bytes
        ("Description_ChR", ctypes.c_char * 32),        # 32 bytes
        ("Unit_ChR", ctypes.c_char * 8)                 # 8 bytes
    ]                                                   # = 136 bytes