[C++-sig] [Py++] ctypes generator produces wrong Python code for function pointers in structs

Dec. 25, 2009

      Hello,

Py++ translates the struct

typedef int cb_fun_t(char *);
struct info {
   cb_fun_t* cb_fun;
   int flag;
};

into the Python Structure

class info(ctypes.Structure):
    """class info"""
info._fields_ = [ #class info
    ("cb_fun", ctypes.POINTER( ctypes.CFUNCTYPE( ctypes.c_int, ctypes.c_char_p ) )),
    ("flag", ctypes.c_int),
]

This is wrong and produces segfaults. The correct version is

class info(ctypes.Structure):
    """class info"""
info._fields_ = [ #class info
    ("cb_fun", ctypes.CFUNCTYPE( ctypes.c_int, ctypes.c_char_p ) ),
    ("flag", ctypes.c_int),
]

I have attached a small example that demonstrates the problem. lib.c is
a small C library, build_api.py creates the broken api.py with Py++.
api_correct.py is the manually corrected API with the correct structure.
call.py demonstrates that the first API segfaults and the second API
works:

$ python call.py 
Calling do_callback with flag=7
do_callback called with flag=7
cb_fun received 'Hello World'
cb_fun returns 42
cb_fun returned 42
do_callback returned 42
Calling do_callback with flag=7
do_callback called with flag=7
Segmentation fault

Please let me know if you can reproduce the problem. It took me quite
some time to figure this out.

Best,

   -Nikolaus

-- 
 »Time flies like an arrow, fruit flies like a Banana.«

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[C++-sig] [Py++] ctypes generator produces wrong Python code for function pointers in structs

Nikolaus Rath