I've spent days stuck on two frustrating issues while trying to load and invoke functions from a third-party C++ DLL that I didn't compile myself. Let me break down exactly what's happening:

Scenario 1: OSError: [WinError 126] When Loading DLL with CDLL() #

When I try to load the DLL directly using ctypes.CDLL(), I get a "specified module not found" error. Here's the code I'm using:

from ctypes import *
__path_aa_Fn_dll__ = r'C:\user\aacad_2017\aa_Functions.dll'  # DLL file path
aa_Fn_dll = CDLL(__path_aa_Fn_dll__)  # load DLL

Full error traceback:

Traceback (most recent call last):
  File "C:/user/aacad_2017/cadClass.py", line 189, in <module>
    aa_Fn_dll = CDLL(__path_aa_Fn_dll__)
  File "C:\Users\user\AppData\Local\Continuum\anaconda3\lib\ctypes\__init__.py", line 348, in __init__
    self._handle = _dlopen(self._name, mode)
OSError: [WinError 126] The specified module could not be found

Scenario 2: AttributeError: Function 'aaBIN2iv' Not Found After Successful Loading #

I tried a workaround using win32api.LoadLibraryEx() to get a handle first, then loading the DLL with CDLL() using that handle. The DLL loads successfully this time, but when I try to call the aaBIN2iv function, I hit an attribute error.

Code to load the DLL:

aa_Fn_dll_handle = win32api.LoadLibraryEx(__path_aa_Fn_dll__, 0, win32con.LOAD_LIBRARY_AS_DATAFILE)  # get DLL handle
aa_Fn_dll = CDLL(__path_aa_Fn_dll__, handle=aa_Fn_dll_handle)  # load DLL

Code to call the function + resulting error:

aa_Fn_dll.aaBIN2iv.restype = c_double  # set function return type
aa_Fn_dll.aaBIN2iv.argtypes = [c_double, c_double, c_double, c_double, c_double, c_double, c_double, c_char_p]  # set function argument types
aa_Fn_dll.aaBIN2iv(10, 10, 10, 10, 10, 10, 10, b"C")  # call DLL function

Traceback (most recent call last):
  File "C:/user/aacadMatlabWrap_2017_new_test/cadClass.py", line 196, in <module>
    aa_Fn_dll.aaBIN2iv.restype = c_double
  File "C:\Users\user\AppData\Local\Continuum\anaconda3\lib\ctypes\__init__.py", line 361, in __getattr__
    func = self.__getitem__(name)
  File "C:\Users\user\AppData\Local\Continuum\anaconda3\lib\ctypes\__init__.py", line 366, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
AttributeError: function 'aaBIN2iv' not found

Attempted Solutions (All Unsuccessful) #

I've tried every fix I can think of, but none have resolved the issues:

• Used Dependency Walker to check for missing dependencies
• Placed all dependent DLLs in the same directory as the target DLL
• Added the DLL's directory to the system PATH environment variable
• Verified the C++ header files use extern "C" to prevent name mangling
• Confirmed the header files use an EXPORTED_FUNCTION keyword for function visibility
• Set Python's working directory to the DLL's location before loading

Working Test Case (Self-Compiled DLL) #

As a sanity check, I compiled my own 64-bit C++ test DLL using Microsoft Visual Studio 2010, and it loads and functions perfectly in Python. Here's the code and output:

Test DLL loading/calling code:

__path_test_dll__ = r'C:\user\dllTest\x64\Release\dllTest.dll'  # test DLL file path
test_dll = CDLL(__path_test_dll__)  # load test DLL
test_dll.fn4.restype = c_void_p  # set test DLL function return type
test_dll.fn4.argtypes = [c_double, c_double, c_double, c_char_p, c_bool]  # set test DLL function argument types
test_dll.fn4(10, 12, 1, b"Pay", True)  # make test DLL function call

Expected console output:

Min_P * Rate == $10 Pay: 1 Min_P: 10 Max_P: 12 Iteration #: 1
Min_P * Rate == $11 Pay: 0 Min_P: 11 Max_P: 12 Iteration #: 2
Min_P * Rate == $12 Pay: 1 Min_P: 12 Max_P: 12 Iteration #: 3
Process finished with exit code 0

I'm really stuck here after spending days on this. Any guidance or troubleshooting directions would be greatly appreciated.

内容的提问来源于stack exchange，提问作者ilbi