使用 ctypes 模块访问用 C 编写的 DLL 时出错

Question

我有一个带有一个函数的 DLL，它得到五个双精度数和一个整数：

__declspec(dllexport)  struct res ITERATE(double z_r,double z_i,double c_r, double c_i, int iterations, double limit)

它重新调整了一个自定义结构，称为 res，它由一个三双数组组成：

struct res {
   double arr[3];
};

要返回值，我这样做：

struct res result;      /*earlier in the code */

result.arr[0] = z_real; /*Just three random doubles*/
result.arr[1] = z_imag;
result.arr[2] = value;
return result;

我已经用 MinGW 编译了它，我正在尝试在 python 中使用它来做这样的事情：

form ctypes import *

z = [0.0,0.0]
c = [1.0,1.0]
M = 2.0

MiDLL = WinDLL("RECERCATOOLS.dll")
MiDLL.ITERATE.argtypes = [c_double, c_double, c_double, c_double,c_int,c_double]
MiDLL.ITERATE(z[0],z[1],c[0],c[1],100,M) #testing out before assigning the result to anything.

但是，每当我尝试使用这些值调用函数时，它都会向我抛出这个：

WindowsError: exception: access violation writing 0x00000000

我也不知道如何捕获我声明的自定义结构并将其每个元素转换为 Python 浮点数。我调查了this PyDocs link，但无济于事。

提前谢谢你。

编辑：

这是使用的原始（根据建议修改）头文件（“mydll.h”）：

#ifndef MYDLL_H
#define MYDLL_H

extern "C" __declspec(dllexport)
#define EXPORT_DLL __declspec(dllexport)

EXPORT_DLL void ITERATE(struct res*, double z_r,double z_i,double c_r, double c_i, int iterations, double limit)


#endif

并且，如果它可能有问题，代码文件（它很短，只有一个功能）：

#include <stdio.h>
#include <complex.h>

struct res {
   double arr[3];
};

void __declspec(dllexport) ITERATE(struct res* result,double z_r,double z_i,double c_r, double c_i, int iterations, double limit)
{
/* The purpose of this function is, given two complex numbers,
   an iteration number and a limit, apply a formula to these
   two numbers for as many iterations as specified.

   If at any iteration the result of the formula is bigger than
   the limit, stop and return the number and the iteration it reached.

   If after iterating they are still inside the limit, return the
   number after all the iterations and the number of iterations
   it has gone through.

   Complex numbers are composed of a real part and an imaginary part,
   and they must be returned separately.
*/
double complex z = z_r + z_i*I;
double complex c = c_r + c_i*I;
int actual_iter;

for (actual_iter = 1; actual_iter <= iterations; actual_iter++)
    {
    z = z*z + c;
    if (cabs(z) > limit)
        {
        double value = actual_iter;
        double z_real = creal(z);
        double z_imag = cimag(z);
        result.arr[0] = z_real;
        result.arr[1] = z_imag;
        result.arr[2] = value;
        }
    }
double value = iterations;
double z_real = creal(z);
double z_imag = cimag(z);
result.arr[0] = z_real;
result.arr[1] = z_imag;
result.arr[2] = value;
}

int main()
{
return 0;
}

Answer 1

返回这样的结构存在问题。并非所有编译器都以相同的方式返回此类结构。我宁愿把函数声明改成这样：

void __declspec(dllexport) ITERATE(struct res* result, double z_r,double z_i, 
    double c_r, double c_i, int iterations, double limit);

这样结构体就在用户的内存中，并且结构体的返回方式没有歧义。

当然，正如 David 所说，您可能必须使用不同的调用约定。