fastddsgen and ros2 gen msg, TypeSupport member m_typeSize id different, why?

[Eternity1987]

file Vec2Image1m.msg ：

shm_msgs/Image1m[2] images

fastddsgen:
fastddsgen -d {src_path} -de final -I . -t {temp_path} -typeros2 -cs {idls_str}

ros2 gen:

fastddsgen m_typeSize value is: 2098236 + 4
ros2 m_typeSize value is: 2098232 + 4

can you help me explain?

[richiware]

@Eternity1987

fastddsgen calculates the maximum size that a type can occupy considering two encodings: XCDRv1 and XCDRv2. ros2 gen only calculates the maximum size for XCDRv1 encoding, which is the difference you see. Your type, by default, is @appendable and 4 extra bytes are needed in XCDRv2 encoding.

Finally, I am moving this conversation to the Support discussion forum as it is not a proper bug in the application.