I have the following
struct.unpack call that fails:
struct.unpack('14x4x2i2xh8x2i', b'\0'*46) Traceback (most recent call last): File "<pyshell#88>", line 1, in <module> struct.unpack('14x4x2i2xh8x2i', b'\0'*46) struct.error: unpack requires a buffer of 48 bytes
I’ve added up the number of bytes required by the format multiple times, and I always come up with a total of 46 bytes. But obviously the error says it’s not enough. Why am I coming up short?
The following does produce the expected output:
struct.unpack('14x4x2i2xh8x2i', b'\0'*48) (0, 0, 0, 0, 0)
struct expects types to be aligned. Since
i is 4 bytes, it’s 2 bytes of padding are assumed to get the offset to a multiple of 4.
You can use the
= flag at the beginning of the format string to indicate that values are packed rather than aligned.
See the documentation of Byte Order, Size, and Alignment. You should probably actually use
< rather than
=, since BMP integers are stored in little-endian format.