Python ctypes cdll.LoadLibrary,实例化一个对象，执行它的方法，私有变量地址被截断

Question

我用c写了一个dll库，用vs2017 64位编译，用python3.6 64位加载试试。但是，对象的成员变量地址被截断为 32 位。

这是我的 sim.c 文件，它被编译为 sim.dll:

class Detector {
public:
    Detector();
    void process(int* pin, int* pout, int n);

private:
    int member_var;
};

Detector::Detector()
{
    memset(&member_var, 0, sizeof(member_var));
    myfile.open("addr_debug.txt");
    myfile << "member_var init address: " << &member_var << endl;
}
void Detector::process(int* pin, int* pout, int n);
{
    myfile << "member_var process address: " << &member_var << endl;
    myfile.close();
}

#define DllExport   __declspec( dllexport )  

extern "C" {
    DllExport Detector* Detector_new() { return new Detector(); }
    DllExport void Detector_process(Detector* det, int* pin, int* pout, int n)
    {
        det->process(pin, pout, n);
    }
}

这是我的 python 脚本：

from ctypes import cdll
lib = cdll.LoadLibrary(r'sim.dll')

class Detector(object):
    def __init__(self):
        self.obj = lib.Detector_new()

    def process(self,pin, pout, n):
        lib.Detector_process(self.obj,pin, pout, n)

detector = Detector()

n = 1024
a = np.arange(n, dtype=np.uint32)
b = np.zeros(n, dtype=np.int32)

aptr = a.ctypes.data_as(ctypes.POINTER(ctypes.c_int))
bptr = b.ctypes.data_as(ctypes.POINTER(ctypes.c_int))

detector.process(aptr, bptr, n)

这是addr_debug.txt中member_var的地址：

member_var init address:    0000025259E123C4
member_var process address: 0000000059E123C4

因此访问它会触发内存访问错误：

OSError: exception: access violation reading 0000000059E123C4

我试图理解这个问题的一些尝试：

将 member_var 定义为 public 而不是私有地址，无济于事，地址仍然被截断。
定义member_var为全局变量，地址就可以了。所以我猜 member_var 地址截断发生在将对象返回到 python 或将对象传递回 dll 时。

Answer 1

始终（正确地）为 C[= 中定义的函数指定 argtypes 和 restype 66=]，否则（C89风格）它们会默认为int（一般32bit），生成！！！未定义的行为 !!!。在 64 位 上，地址（大于 2 GiB）将被 t运行分类（这正是你正在经历的）。查看了解更多详情。

此外，当运行遇到问题时，不要忘记 [Python 3.Docs]: ctypes - A foreign function library for Python。

下面是您的代码的改编版本。

detector.cpp:

#include <stdio.h> #include <memory.h> #include <fstream> #define C_TAG "From C" #define PRINT_MSG_2SP(ARG0, ARG1) printf("%s - [%s] (%d) - [%s]: %s: 0x%0p\n", C_TAG, __FILE__, __LINE__, __FUNCTION__, ARG0, ARG1) using std::endl; std::ofstream outFile; class Detector { public: Detector(); void process(int *pIn, int *pOut, int n); private: int m_var; }; Detector::Detector() : m_var(0) { outFile.open("addr_debug.txt"); outFile << "m_var init address: " << &m_var << endl; PRINT_MSG_2SP("&m_var", &m_var); } void Detector::process(int *pIn, int *pOut, int n) { outFile << "m_var process address: " << &m_var << endl; outFile.close(); PRINT_MSG_2SP("&m_var", &m_var); } #define SIM_EXPORT __declspec(dllexport) #if defined(__cplusplus) extern "C" { #endif SIM_EXPORT Detector *DetectorNew() { return new Detector(); } SIM_EXPORT void DetectorProcess(Detector *pDet, int *pIn, int *pOut, int n) { pDet->process(pIn, pOut, n); } SIM_EXPORT void DetectorDelete(Detector *pDet) { delete pDet; } #if defined(__cplusplus) } #endif

code.py:

import sys from ctypes import CDLL, POINTER, \ c_int, c_void_p import numpy as np sim_dll = CDLL("./sim.dll") detector_new_func = sim_dll.DetectorNew detector_new_func.restype = c_void_p detector_process_func = sim_dll.DetectorProcess detector_process_func.argtypes = [c_void_p, POINTER(c_int), POINTER(c_int), c_int] detector_delete_func = sim_dll.DetectorDelete detector_delete_func.argtypes = [c_void_p] class Detector(): def __init__(self): self.obj = detector_new_func() def process(self, pin, pout, n): detector_process_func(self.obj, pin, pout, n) def __del__(self): detector_delete_func(self.obj) def main(): detector = Detector() n = 1024 a = np.arange(n, dtype=np.uint32) b = np.zeros(n, dtype=np.int32) aptr = a.ctypes.data_as(POINTER(c_int)) bptr = b.ctypes.data_as(POINTER(c_int)) detector.process(aptr, bptr, n) if __name__ == "__main__": print("Python {:s} on {:s}\n".format(sys.version, sys.platform)) main()

备注:

正如我在开头所说，问题是 argtypes 和 restype 没有被指定（例如 DetectorNew ：评论detector_new_func.restype = c_void_p，你会运行再次陷入问题）

问题中的代码缺少部分（#includes，imports，...），还有一些语法错误，因此它无法编译，因此不遵循 [SO]: How to create a Minimal, Complete, and Verifiable example (mcve) 准则。请在询问
时确保有mcve
你分配的对象（new Detector()），也必须被释放（否则会产生内存泄漏），所以我添加了一个函数（DetectorDelete - 这样做），这是从 (Python) Detector 调用的析构函数

其他（非关键）更改（标识符重命名、一些重构、打印到 stdout、...）

输出:

(py35x64_tes1) e:\Work\Dev\Whosebug\q052268294>"c:\Install\x86\Microsoft\Visual Studio Community15\vc\vcvarsall.bat" x64 (py35x64_test) e:\Work\Dev\Whosebug\q052268294>dir /b code.py detector.cpp (py35x64_test) e:\Work\Dev\Whosebug\q052268294>cl /nologo /DDLL /EHsc detector.cpp /link /DLL /OUT:sim.dll detector.cpp Creating library sim.lib and object sim.exp (py35x64_test) e:\Work\Dev\Whosebug\q052268294>dir /b code.py detector.cpp detector.obj sim.dll sim.exp sim.lib (py35x64_test) e:\Work\Dev\Whosebug\q052268294>"e:\Work\Dev\VEnvs\py35x64_test\Scripts\python.exe" ./code.py Python 3.5.4 (v3.5.4:3f56838, Aug 8 2017, 02:17:05) [MSC v.1900 64 bit (AMD64)] on win32 From C - [detector.cpp] (28) - [Detector::Detector]: &m_var: 0x0000020CE366E270 From C - [detector.cpp] (34) - [Detector::process]: &m_var: 0x0000020CE366E270

Python ctypes cdll.LoadLibrary,实例化一个对象，执行它的方法，私有变量地址被截断

Python ctypes cdll.LoadLibrary, instantiate an object, execute its method, private variable address truncated

python

windows

dll

ctypes