ctype problem

[Grimson]

hello out there,
I have a problem with c-types.
I made a c-library, which expects a pointer to a self defined structure.

let the funtion call myfunction(struct interface* iface)

and the struct:
struct interface
{
int a;
int b;
char *c;
}

the Python ctype port of this structur would be:

class INTERFACE(Structure):
_fields_ = [("a" c_int),
("b", c_int),
("c", c_char)]

in my python-struct a create a instance of INTERFACE

myiface = INTERFACE()
myiface.a = ctypes.c_int(80)
myiface.b = ctypes.c_int(22)
....
than I make a pointer onto it.
p_iface = ctypes.pointer(myiface)
and I tried it also with a reference
r_iface = ctypes.byref(myiface)

but neither myclib.myfunction(p_iface) nor myclib.myfunction(r_iface)
works properly. The function is been called but it reads only zeros (0)
for each parameter (member in the struct).

Where is my fault?

Thank you..

sincerely chris

 

[Aaron Brady]

hello out there,
I have a problem with c-types.
I made a c-library, which expects a pointer to a self defined structure.

let the funtion call myfunction(struct interface* iface)

and the struct:
struct interface
{
    int a;
    int b;
    char *c;

}

the Python ctype port of this structur would be:

class INTERFACE(Structure):
    _fields_ = [("a"         c_int),
                      ("b",        c_int),
                      ("c",         c_char)]

in my python-struct a create a instance of INTERFACE

myiface = INTERFACE()
myiface.a = ctypes.c_int(80)
myiface.b = ctypes.c_int(22)
...
than I make a pointer onto it.
p_iface = ctypes.pointer(myiface)
and I tried it also with a reference
r_iface = ctypes.byref(myiface)

but neither myclib.myfunction(p_iface) nor myclib.myfunction(r_iface)
works properly. The function is been called but it reads only zeros (0)
for each parameter (member in the struct).

Where is my fault?

Thank you..

sincerely chris

Did you remember to define myclib.myfunction.argtypes= [ INTERFACE ] ?

 

[Mark Tolonen]

hello out there,
I have a problem with c-types.
I made a c-library, which expects a pointer to a self defined structure.

let the funtion call myfunction(struct interface* iface)

and the struct:
struct interface
{
int a;
int b;
char *c;

}

the Python ctype port of this structur would be:

class INTERFACE(Structure):
_fields_ = [("a" c_int),
("b", c_int),
("c", c_char)]

in my python-struct a create a instance of INTERFACE

myiface = INTERFACE()
myiface.a = ctypes.c_int(80)
myiface.b = ctypes.c_int(22)
...
than I make a pointer onto it.
p_iface = ctypes.pointer(myiface)
and I tried it also with a reference
r_iface = ctypes.byref(myiface)

but neither myclib.myfunction(p_iface) nor myclib.myfunction(r_iface)
works properly. The function is been called but it reads only zeros (0)
for each parameter (member in the struct).

Where is my fault?

I believe you want ("c",c_char_p), although I don't get the same error as
you describe when I use c_char. Below is my working code (Python 2.6.1 and
Visual Studio 2008):

---- x.py ----
from ctypes import *

class INTERFACE(Structure):
_fields_ = [
('a',c_int),
('b',c_int),
('c',c_char)
]

x = CDLL('x.dll')
i = INTERFACE()
i.a = 1
i.b = 2
i.c = 'hello'
x.myfunction(byref(i))

---- cl /LD /W4 x.c -> x.dll ----
#include <stdio.h>

struct interface
{
int a;
int b;
char* c;
};

__declspec(dllexport)
void myfunction(struct interface* iface)
{
printf("%d %d %s\n",iface->a,iface->b,iface->c);
}

-Mark