python - ctypes cdecl gives 4 bytes missing when calling gcc compiled dll returning a struct -

i have c library (chipmunk) want call using ctypes. however, fails on functions return struct?

the error

file "qw.py", line 19, in <module> b = cpbbnew3(1,2,3,4) valueerror: procedure called not enough arguments (4 bytes missing) or wrong calling convention 

this (relevant) c-code: in cpbb.h

typedef struct cpbb {     cpfloat l, b, r ,t; } cpbb; cpbb cpbbnew3(cpfloat l, cpfloat b, cpfloat r, cpfloat t); 

in cpbb.c

cpbb cpbbnew3(cpfloat l, cpfloat b, cpfloat r, cpfloat t) {     cpbb bb = {l, b, r, t};     return bb; } 

compiled

gcc -o3 -std=gnu99 -shared -c

gcc -o3 -std=gnu99 -shared -s

then python looks

from ctypes import *  chipmunk_lib = cdll.loadlibrary('''c:/code/pymunk/trunk/pymunk/chipmunk.dll''')  class cpbb(structure):     pass cpbb._pack_ = 4 cpbb._fields_ = [     ('l', c_double),     ('b', c_double),     ('r', c_double),     ('t', c_double), ]  cpbbnew3 = chipmunk_lib.cpbbnew3 cpbbnew3.restype = cpbb cpbbnew3.argtypes = [c_double, c_double, c_double, c_double]  b = cpbbnew3(1,2,3,4) 

this particular example works if compile -mrtd , use windll (using stdcall). using stdcall on whole library creates segmentation faults in other parts of library when compiled optimizations , newish version of gcc why nice cdecl working.

depending on size of struct , compiler/platform, cdecl may return structs passing hidden pointer caller-allocated struct before normal parameters. try following:

b = cpbb() cpbbnew3(byref(b),1,2,3,4)