将结构从c ++ dll返回到Python [英] Returning struct from c++ dll to Python

问题描述

我试图返回结构，所以我可以在Python中使用它。我是初学者程序员，所以请向我解释我做错了什么。我成功地返回简单的ctypes更早（bool，unsigned int），但结构对我来说太复杂了。这是我的：

I'm trying to return structure so I can use it in Python. I am beginner programmer so please explain me what am I doing wrong. I've succeeded to return simple ctypes earlier (bool, unsigned int) but struct is too complicated for me. This is what I have:

DLLAPI.h

#define DLLAPI extern "C" __declspec(dllexport)
...
DLLAPI myStruct* DLLApiGetStruct();

DLLAPI.cpp

DLLAPI.cpp

EDIT1：而不是TString，struct成员类型是wchar_t *现在，但是我得到的错误是相同的

...
typedef struct myStruct{
    wchar_t* id; 
    wchar_t* content; 
    wchar_t* message;
} myStruct;

DLLAPI myStruct* DLLApiGetStruct(){
    myStruct* test = new myStruct();
    test->id = _T("some id"); 
    test->content = _T("some content"); 
    test->message = _T("some message");
    return test;
}

这里是我的Python代码：

here is my Python code:

...
class TestStruct(Structure):
    _fields_ = [
        ("id", c_wchar_p),
        ("content", c_wchar_p),
        ("message", c_wchar_p)
        ]
class SomeClass(object):
    ....  
    def test(self):
        myDLL = cdll.LoadLibrary('myDLL.dll')
        myDLL.DLLApiGetStruct.restype = TestStruct
        result = myDLL.DLLApiGetStruct()
        print "result type: ", type(result)
        print "-"*30
        print "result: ",result
        print "-"*30
        print result.id # line 152

这是我得到的：

    result type:  <class 'Foo.TestStruct'>
    ------------------------------
    result:  <Foo.TestStruct object at 0x027E1210>
    ------------------------------
    Traceback (most recent call last):
    ....
    ....
    ....
    line 152, in test
        print result.id
    ValueError: invalid string pointer 0x00000002

TString我使用的是std :: wstring

TString I've used is std::wstring

应该输入myStruct是指针还是东西，而不是TString？

Should type in myStruct be pointers or something instead TString? Please help me, I've spend 5 days trying to make this work.

推荐答案

正如其他人解释的那样，问题的版本1的问题是使用std :: string这不是一个有效的interop的类型。

As the others explained, the problem with version 1 of the question is the use of std::string which is not a valid type for interop.

看看版本2的问题，你的C ++和Python声明不匹配。 C ++代码返回一个指向结构体的指针，但Python代码期望结构体通过值返回。

Looking at version 2 of the question, your C++ and Python declarations do not match. The C++ code returns a pointer to the struct, but the Python code expects the struct to be returned by value.

你可以改变C ++或Python来匹配另一个。

You could change either C++ or Python to match the other.

C ++

DLLAPI myStruct DLLApiGetStruct()
{
    myStruct result;
    result.id = L"some id";
    result.content = L"some content";
    result.message = L"some message";  
    return result;
}

Python

myDLL.DLLApiGetStruct.restype = POINTER(TestStruct)

显然，你只能应用这些更改之一！

Obviously you must apply only one of these changes!

请注意，在C ++代码中，我选择使用带有L前缀的显式宽字符串，而不是_T（）宏。前者匹配wchar_t *，后者是你使用TCHAR。我不会推荐TCHAR这些天，除非你需要支持Win98。

Note that in the C++ code I chose to use explicit wide strings with the L prefix rather than the _T() macro. The former matches wchar_t* and the latter is what you use with TCHAR. I would not recommend TCHAR these days, unless you need to support Win98.

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