Python：简单的ctypes dll加载产生错误

问题描述

我从并运行调用.cpp工作正常。现在，试图在IPython中加载这样的类型，如

  import ctypes 
 lib = ctypes.WinDLL（'MathFuncsDll。 dll'）
  

在正确的文件夹中产生

UnicodeDecodeError：'ascii'编解码器无法解码28位字节0xe4：ordinal不在范围（128）

我该怎么改？嗯，这可能是Win 7 64bit，而有些32bit的DLL还是正确的？稍后我再检查一下。

解决方案

ctypes 不能与C ++一起工作，MathFuncsDLL示例被写入。

相反，写入C或至少导出C接口：

  #ifdef __cplusplus 
 externC{
 #endif 
 
 __declspec（dllexport ）double Add（double a，double b）
 {
 return a + b; 
} 
 
 #ifdef __cplusplus 
} 
 #endif 
  

另请注意，调用约定默认为 __ cdecl ，因此使用 CDLL 而不是 WinDLL （使用 __ stdcall 调用约定）：

 >>> import ctypes 
>>> dll = ctypes.CDLL（'server'）
>>> dll.Add.restype = ctypes.c_double 
>>> dll.Add.argtypes = [ctypes.c_double，ctypes.c_double] 
>>> dll.Add（1.5,2.7）
 4.2 
  

I created the MathFuncsDll.dll from MSDN DLL example and running the calling .cpp worked fine. Now, trying to load this in IPython with ctypes like

import ctypes
lib = ctypes.WinDLL('MathFuncsDll.dll')

being in the correct folder yields

UnicodeDecodeError: 'ascii' codec can't decode byte 0xe4 in position 28: ordinal not in range(128)

Similarly in Python shell this yields

WindowsError: [Error 193] %1 is not a valid Win32 application

What should I change? Hm, it might be Win 7 64bit vs. some 32bit dll or something right? I'll check later when I've time again.

解决方案

ctypes doesn't work with C++, which the MathFuncsDLL example is written in.

Instead, write in C, or at least export a "C" interface:

#ifdef __cplusplus
extern "C" {
#endif

__declspec(dllexport) double Add(double a, double b)
{
    return a + b;
}

#ifdef __cplusplus
}
#endif

Also note that the calling convention defaults to __cdecl, so use CDLL instead of WinDLL (which uses __stdcall calling convention):

>>> import ctypes
>>> dll=ctypes.CDLL('server')
>>> dll.Add.restype = ctypes.c_double
>>> dll.Add.argtypes = [ctypes.c_double,ctypes.c_double]
>>> dll.Add(1.5,2.7)
4.2

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