在Windows上使用ctypes在python中包装c ++函数：未找到函数 [英] Wrapping c++ functions in python with ctypes on windows : function not found
问题描述
我需要运行一系列python脚本来计算各种脚本，这些脚本运行良好，但是其中一个运行速度非常慢，必须使用C ++来完成。
C ++代码已准备就绪，但是我需要找到一种从python调用C ++函数并获取返回值的方法。
I need to run a series of python scripts calculating various scripts, that are working fine, but one of them runs very slowly and has to be done in C++. The C++ code is ready, but I need to find a way to call the C++ function from the python and get the return value.
我找到了有关SWIG，但没有在Visual Studio的Windows上运行（由于其他限制，我必须在Windows的VS中运行）。我发现对于具有标准输入和输出值的非常简单的功能，ctypes更加容易。
I found information about SWIG, but didn't get it to work on Windows with Visual Studio (I have to do it in VS on Windows, because of other constraints). I found ctypes much easier for my very simple function with standart input and output values.
因此，我对ctypes进行了许多测试，尝试了所有可以在网上找到的示例，并且每次，都会发生什么事，我可以加载dll（使用Visual Studio 2012编译器构建），但是当我尝试在python中调用该函数时，它就会消失：
So I did many tests with ctypes, tried all the examples I could find online, and each and every time, what happens is that I can load the dll (built with visual studio 2012 compiler) but when I try calling the function in python, it just goes :
Traceback (most recent call last):
File "test.py", line 3, in <module>
print maLib.plop()
File "C:\Python27\lib\ctypes\__init__.py", line 378, in __getattr__
func = self.__getitem__(name)
File "C:\Python27\lib\ctypes\__init__.py", line 383, in __getitem__
func = self._FuncPtr((name_or_ordinal, self))
AttributeError: function 'plop' not found
python代码是（test.py）：
The python code is (test.py) :
from ctypes import cdll
lib = cdll.LoadLibrary('test')
print lib.plop()
C ++代码是（test.cpp，编译为test.dll，Visual Studio设置为dll ）：
The C++ code is (test.cpp, compiled as test.dll, Visual Studio set to build as dll) :
extern "C"
{
int plop();
}
int plop() { return 4; }
如您所见，我试图使其尽可能地简单，以避免出现细节失败。我已经阅读了python ctypes帮助，以及有关如何使用ctypes的教程，尝试使用与它们完全相同的代码，但是由于我使用的是Visual Studio / windows，而其他大多数用户都在使用linux，因此我不得不稍作调整。
所有文件都在同一个文件夹中。
As you can see, I tried to make it as simple as possible, to avoid details making it fail. I have read the python ctypes help, and tutorials on how to use ctypes, trying exactly the same codes as them, but I had to adapt a bit because I am using Visual Studio / windows and most of the other users are using linux. All of the files are in the same folder.
我尝试了多种加载库的方式：LoadLibrary（'./ name.dll'）， WinDLL（'name.dll'），为函数指定其他名称，无效的返回类型等...
I have tried multiple ways of loading the library : LoadLibrary('./name.dll'), WinDLL('name.dll'), giving the function a different name, void return type, etc...
您认为我应该使用SWIG吗？我的问题是明显的初学者错误吗？我是一名学生，并且对大多数正在使用的东西都是陌生的，但是即使我只是为了完成某项任务，也为此付出了很多努力。
使用SWIG时，我不得不用函数指针或引用包装，所以我认为这是问题所在，这使我想尝试一个更简单的解决方案。
Do you think I should use SWIG ? Is my problem an obvious beginner mistake ? I am a student, and new to most of what I'm using, but I put a lot of effort in this, even if I just need it for a particular single task. When using SWIG, I had to make a wrapper with function pointers, or references, so I thought this was the problem, which made me want to try a simpler solution.
我正在使用：Python 2.7.7，Visual Studio 2012，Windows 8.1
I am using : Python 2.7.7, Visual Studio 2012, Windows 8.1
在此先感谢
推荐答案
您的Python报告的错误非常清楚。
The error reported by your Python is very clear.
函数'plop'不是找到
function 'plop' not found
这意味着DLL不会导出该名称的函数。因此，您需要导出功能。使用.def文件，或使用 __ declspec（dllexport）：
This means that the DLL does not export a function of that name. So, you need to export the function. Either with a .def file, or using __declspec(dllexport):
extern "C"
{
__declspec(dllexport) int plop();
}
要检查您的DLL以调试此类问题，请使用 dumpbin 或Dependency Walker。
To inspect your DLL to debug issues like this, use dumpbin or Dependency Walker.
请注意，由于未指定调用约定，因此默认值为 __ cdecl 被使用。这意味着 cdll 在 ctypes 方面是正确的。
Note that since you do not specify calling convention, the default of __cdecl is used. That means that cdll is correct on the ctypes side.
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