Re: [ctypes-users] Pointers to int or Char*

[Thomas H. <th...@py...>]

"Mark McMahon" <mar...@eu...> writes:

> Hi Tomas,
> 
> It didn't work ;(
> (python 2.2, CVS ctypes from a couple of days ago)

Mark, thanks for the report. The code I posted was buggy, but it was
somewhat funny to track down.

For now, here is code that works, both for ANSI and UNICODE.

The problem was that c_char_p.from_address(...) was not correct, because
it expects an address where a 'pointer to a string' is stored, but it
receives the address where the first character is stored ;-(.

The deeper problem was (is?) that an access violation in the callback
function (my_enum_proc) is catched by the win32 structured exception
handling handler for the EnumResourceTypesA() call, but without
releasing Python's global interpreter lock again, so the code keeps
waiting for the gil, until you interrupt it with CTRL-Break.

> I also was wondering if there was any easy way to pass python objects to
> functions (for example the 3rd parameter to EnumResourceTypes), I did
> use the method that you outlined in the thread "Converting instances to
> address and back". But that seems like hackery, and I am wondering if
> there is an easier way. 

I think the 3rd parameter in the win32 enum... functions is for
languages less powerful than python - those which don't have bound
methods.

In Python, I would use a bound method as the my_enum_proc, which will
then automatically receive the 'self' parameter, and you use the
instance variables.


Thomas

#--------------------------------------
from ctypes import *
import ctypes # for _LoadLibrary
import os
import os.path

class RES_A(Union):
    _fields_ = [("int", c_int),
                ("str", c_char_p)]

    def _get_value(self):
        if self.int & 0xFFFF0000:
            return self.str
        return self.int
    value = property(_get_value)

class RES_W(RES_A):
    _fields_ = [("int", c_int),
                ("str", c_wchar_p)]

def my_enum_proc(hModule, lpszType, lParam):
    print repr(lpszType.value)
    return 1

EnumResTypeProcW = WINFUNCTYPE(c_int, c_int, RES_W, c_int)
EnumResTypeProcA = WINFUNCTYPE(c_int, c_int, RES_A, c_int)

lib = ctypes._LoadLibrary(os.path.join(r"c:\windows\\system32", r"shell32.dll"))

print "-"*15, "UNICODE", "-"*15
windll.kernel32.EnumResourceTypesW(lib, EnumResTypeProcW(my_enum_proc), 0)
print "-"*15, "ANSI", "-"*15
windll.kernel32.EnumResourceTypesA(lib, EnumResTypeProcA(my_enum_proc), 0)
#----------------------------------------

On my system, this code prints:
--------------- UNICODE ---------------
u'AVI'
u'REGINST'
u'TYPELIB'
u'UIFILE'
1
2
3
4
5
6
9
12
14
16
23
24
--------------- ANSI ---------------
'AVI'
'REGINST'
'TYPELIB'
'UIFILE'
1
2
3
4
5
6
9
12
14
16
23
24