将指向动态分配变量的指针传递给要删除的函数

Question

libtestm.dll 代码

#pragma once
#define EXPORT extern "C" __declspec(dllexport)
#include <iostream>
#include <vector>

class TestValue
{
public:
    std::vector<int> v;
    TestValue()
    {
        for (size_t i = 0; i < 10; i++)
        {
            v.push_back(i);
        }
    }
    ~TestValue()
    {
        std::cout << "Deteled Test Value" << std::endl;
    }
};

EXPORT TestValue *TestReturn()
{
    return new TestValue();
}

EXPORT size_t TestData(TestValue *pt, int **array)
{
    *array = pt->v.data();
    return pt->v.size();
}

EXPORT void TestDelete(TestValue *pt)
{
    if(pt)
    {
        delete pt;
    }
}

TestLib.py

import os, sys
from ctypes import *
import Libs.Utils as u

__dllname__: str = 'libtestm.dll'

__dllfile__: str = None
__dll__: cdll = None
__dllfile__, __dll__ = u.FindLoadDll(__dllname__, __file__) # get dll from this method

if __name__ == "__main__":
    v = __dll__.TestReturn()
    __dll__.TestDelete(v)

运行此代码时的控制台输出

Deteled Test Value
Traceback (most recent call last):
  File "d:\MyProjects\GitRepo\CodePython\Dlls\TestLib.py", line 31, in <module>
    __dll__.TestDelete(v)
OSError: exception: access violation reading 0x00000000A20E2490

c++标准库与python的ctypes一起使用很困难，所以我尝试通过将它包装在一个类中来使用它。成功释放指向动态分配变量的指针，但发生错误。请让我知道我错了什么。谢谢。

Answer 1

这是大多数ctypes 用户的标准错误。 ctypes 如果未指定，则假定参数类型，通常是 c_int 或参数指针，c_int 用于返回类型。由于 TestValue* 是 64 位的，c_int 的返回值是 32 位并截断它。解决方案是养成始终为使用的每个函数指定.argtypes 和.restype 的习惯：

test.cpp:

#pragma once
#define EXPORT extern "C" __declspec(dllexport)
#include <iostream>
#include <vector>

class TestValue {
public:
    std::vector<int> v;
    TestValue() {
        for (int i = 0; i < 10; i++)
            v.push_back(i);
    }
    ~TestValue() {
        std::cout << "Deleted Test Value" << std::endl;
    }
};

EXPORT TestValue *TestReturn() {
    return new TestValue();
}

EXPORT size_t TestData(TestValue *pt, int **array) {
    *array = pt->v.data();
    return pt->v.size();
}

EXPORT void TestDelete(TestValue *pt) {
    if(pt)
        delete pt;
}

test.py：

from ctypes import *

dll = CDLL('./test')
dll.TestReturn.argtypes = ()
dll.TestReturn.restype = c_void_p
dll.TestData.argtypes = c_void_p,POINTER(POINTER(c_int))
dll.TestData.restype = c_size_t
dll.TestDelete.argtypes = c_void_p,
dll.TestDelete.restype = None

v = dll.TestReturn()
data = POINTER(c_int)()
size = dll.TestData(v,byref(data))
print(data[:size])
dll.TestDelete(v)

输出：

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Deleted Test Value