Python ctypes。获取二维数组

Question

我有这个 c++ 代码：

#define DLLEXPORT extern "C"

DLLEXPORT double **points(unsigned N, unsigned D)
{

double **POINTS = new double * [N];
for (unsigned i=0;i<=N-1;i++) POINTS[i] = new double [D];
for (unsigned j=0;j<=D-1;j++) POINTS[0][j] = 0;

// do some calculations, f.e:
// POINTS[i][j] = do_smth()
//


return POINTS
}

我使用这个命令编译的：

g++ -shared gpoints.cc -o gpoints.so -fPIC

现在我想使用 ctypes 从 python 调用这个函数。我是这样尝试的：

mydll = ctypes.cdll.LoadLibrary('/.gpoints.so')
func = mydll.points
mytype = c.c_double * 3 * 10
func.restype = mytype
arr = func(10, 3)
print(arr)

当我尝试运行它时，我得到：

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc
[1]    2794 abort      python3 test.py

那么，如何从 Python 中正确调用这个函数呢？

附：我“按原样”得到了这个库，所以最好在不重写 c++ 代码的情况下使用它。

Answer 1

您的restype 等价于double[10][3]，但它实际返回的是double**：

#!python3.6
import ctypes as c
dll = c.CDLL('test')
dll.points.argtypes = c.c_int,c.c_int
dll.points.restype = c.POINTER(c.POINTER(c.c_double))
arr = dll.points(10,3)
for i in range(10):
    for j in range(3):
        print(f'({i},{j}) = {arr[i][j]}')

我使用以下 DLL 代码进行测试（Windows）：

extern "C" __declspec(dllexport)
double **points(unsigned N, unsigned D)
{
    double **POINTS = new double * [N];
    for (unsigned i=0;i<=N-1;i++)
    {
        POINTS[i] = new double [D];
        for(unsigned j=0;j<=D-1;j++)
            POINTS[i][j] = i*N+j;
    }
    return POINTS;
}

输出：

(0,0) = 0.0
(0,1) = 1.0
(0,2) = 2.0
(1,0) = 10.0
(1,1) = 11.0
(1,2) = 12.0
(2,0) = 20.0
(2,1) = 21.0
   :