ctypes and misaligned doubles

[Jan Roelens]

Dear python experts,

How can I change the alignment of types in the ctypes package? I have
a library that was built with gcc using the -malign-double option. I
also have python code that can create ctypes wrapper code from the
include files for that library. The problem is that structs that
contain fields of type double are not correctly wrapped half of the
time. This is because ctypes assumes an alignment of 4 (on a 32-bit
platform) for the double type, while the library I'm wrapping uses an
alignment of 8 for these doubles.

Is there a way to change the alignment of a ctypes type without
recompiling the whole ctypes package? If I can't change it, is there a
way to define my own type based on c_double but with a different
alignment?

Regards,
Jan

 

[Thomas Heller]

Dear python experts,

How can I change the alignment of types in the ctypes package? I have
a library that was built with gcc using the -malign-double option. I
also have python code that can create ctypes wrapper code from the
include files for that library. The problem is that structs that
contain fields of type double are not correctly wrapped half of the
time. This is because ctypes assumes an alignment of 4 (on a 32-bit
platform) for the double type, while the library I'm wrapping uses an
alignment of 8 for these doubles.

To force an alignment that is smaller than the native alignment, you
can use the _pack_ attribute in your Structure definitions.

http://docs.python.org/library/ctypes.html?highlight=_pack_#ctypes.Structure._pack_

To force an alignment that is larger than the native alignment, you
must use padding.

Is there a way to change the alignment of a ctypes type without
recompiling the whole ctypes package? If I can't change it, is there a
way to define my own type based on c_double but with a different
alignment?

No.

Thomas