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OS: Windows 2003STD x64 en
I have try to call python method from c++ dll by "WINFUNCTYPE".
But the 4th parameter is always None or 0 if the type is int or void* (float is works fine).
Following is the part of source code:
==code==========================================
import sys
from ctypes import *
windll.LoadLibrary("testPy2.dll")
#########################################
def test3(param1,param2,param3,param4,param5,param6,param7,param8,param9,param10):
 print("================")
 print(param1)
 print(param2)
 print(param3)
 # the 4th param4 is always 0.
 print(param4)
 print(param5)
 print(param6)
 print(param7)
 print(param8)
 print(param9)
 print(param10)
 print("================")
 return 20
 
C_METHOD_TYPE4 = WINFUNCTYPE(c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32)
windll.testPy2.fntestPy7(9,C_METHOD_TYPE4(test3))
==code==========================================
To my knowledge, both visual c++ and gcc use registers for the first few parameters, and then after that use the stack. Maybe this is the reason.
I have attached some simple codes for reproduce this issue.
issues
 - testPy2 <- source code of the dll
 - test.py <- python file to reproduce the issue
 - testPy2.dll <- the dll to reproduce the issue

Please reproduce this issue by 64bit Python.

Note:
This issue also occurs on other 64 bit windows OS(i.e. windows xp 64bit)
Load "testPy2.dll" needs vc++ runtime library (http://download.microsoft.com/download/2/d/6/2d61c766-107b-409d-8fba-c39e61ca08e8/vcredist_x64.exe)
Update "testPy2.dll", use this to reproduce the issue.
python code:
import sys
from ctypes import *
windll.LoadLibrary("testPy2.dll")
#########################################
def test3(param1,param2,param3,param4,param5,param6,param7,param8,param9,param10):
 print("================")
 print(param1)
 print(param2)
 print(param3)
 print(param4)
 print(param5)
 print(param6)
 print(param7)
 print(param8)
 print(param9)
 print(param10)
 print("================")
 return 20
 
C_METHOD_TYPE4 = WINFUNCTYPE(c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32)
windll.testPy2.fntestPy7(9,C_METHOD_TYPE4(test3))
#########################################
def test4(param1,param2,param3,param4,param5,param6,param7,param8,param9,param10):
 print("================")
 print(param1)
 print(param2)
 print(param3)
 print(param4)
 print(param5)
 print(param6)
 print(param7)
 print(param8)
 print(param9)
 print(param10)
 print("================")
 return 20
 
C_METHOD_TYPE5 = WINFUNCTYPE(c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32, c_int32)
windll.testPy2.fntestPy8(10,C_METHOD_TYPE5(test4))
#########################################
def test5(param1,param2,param3,param4,param5,param6,param7,param8,param9,param10):
 print("================")
 print(param1)
 print(param2)
 print(param3)
 print(param4)
 print(param5)
 print(param6)
 print(param7)
 print(param8)
 print(param9)
 print(param10)
 print("================")
 return 20
 
C_METHOD_TYPE6 = WINFUNCTYPE(c_int32, c_float, c_float, c_float, c_float, c_float, c_float, c_float, c_float, c_float, c_float)
windll.testPy2.fntestPy9(11,C_METHOD_TYPE6(test5))

Probably this issue is duplicate of #9266.

I don't have x64 machine, so I cannot test this.
So this is just an idea.
It seems
Modules/_ctypes/libffi_msvc is a bit old.
Modules/_ctypes/libffi/src/x86 is newer.
Maybe this issue can be fixed by using newer one?
Thank you.

I tested this issue in Python2.7.1, Python3.1.3 and Python 3.2rc1. It's still can reproduce. Would you please check this "Callback functions" issue?

The provided example has two problems: The DLL should be loaded as cdll, not windll. C_METHOD_TYPE4 uses c_int32 as parameter type while pyFunc4Type in testPy2.cpp uses LPVOID (64 bit on win-amd64). Even with those corrections the issue remains.

yes, I tried lots of types. The issue still happens. The same case in Ubuntu and Mac were works well.

The patch attached to #8275 fixes this issue and possibly also #9266.
Tested with Python 2.7.1 64 bit on Windows 7.

wow~~~ It works on my PC too (Windows 2003 STD x64). Thanks.

Disabling optimizations doesn't really fix the issue, just hides it, for now.
The problem was an uninitialized variable. Attached is the patch that fixes it.

Thanks, this issue has been fixed. :-)
fixing revisions:
r88284 (3.2), r88285 (3.1) and r88286 (2.7)