从Python(ctypes)到C的指针以保存函数输出 [英] Pointer from Python (ctypes) to C to save function output

问题描述

我是Python的C集成的新手.我目前正在使用 ctypes 将.dll库包装到我的Python代码中，并且在传递指针以保存特定函数的输出时遇到问题.

I'm new to C integration in Python. I'm currently wrapping a .dll library into my Python code using ctypes and I'm having issues passing a pointer to save the output of a particular function.

我的C函数具有以下结构:

My C function has the following structure:

函数(int * w，int * h，无符号short * data_output)

function (int* w, int* h, unsigned short* data_output)

其中 h 和 w 是输入，而 data_output 是大小为(wxh，1)的数组.

Where h and w are inputs and data_output is an array of size (w x h, 1).

我能够通过创建 zeros(wxh，1)数组并使用 libpointer('uint16Ptr'零(wxh，1)).

I was able to successfully integrate and retrieve results from the function in Matlab by creating a zeros(w x h,1) array and passing it as a pointer using libpointer('uint16Ptr', zeros(w x h, 1)).

如何在Python中做到这一点?

How can I do that in Python?

对于其他函数，其输出为 int * 类型，我能够使用 create_string_buffer 成功检索值.但是我没有设法使它适用于这个.

For other functions, where the output was of int* type I was able to successfully retrieve the values using create_string_buffer. But I haven't managed to make it work for this one.

谢谢.

推荐答案

根据 [SO]:如何创建最小的，完整的和可验证的示例(mcve)，您的问题不包含基本信息(例如您的尝试).请确保在接下来的内容中予以更正.

According to [SO]: How to create a Minimal, Complete, and Verifiable example (mcve), your question doesn't contain basic info (e.g. your attempts). Make sure to correct that in the next ones.

此外， [Python 3]:ctypes-外部函数库对于Python .

这是一个虚拟的例子，说明了这个概念.

Here's a dummy example that illustrates the concept.

dll.c :

#if defined(_WIN32)
#  define DLL_EXPORT __declspec(dllexport)
#else
#  define DLL_EXPORT
#endif


DLL_EXPORT int function(int w, int h, unsigned short *pData) {
    int k = 1;
    for (int i = 0; i < h; i++)
        for (int j = 0; j < w; j++, k++)
            pData[i * w + j] = k;
    return w * h;
}

code.py :

#!/usr/bin/env python3

import sys
import ctypes


DLL = "./dll.so"


def print_array(data, h, w):
    for i in range(h):
        for j in range(w):
            print("{:2d}".format(data[i * w + j]), end=" ")
    print()


def main():
    dll_dll = ctypes.CDLL(DLL)
    function_func = dll_dll.function
    function_func.argtypes = [ctypes.c_int, ctypes.c_int, ctypes.POINTER(ctypes.c_ushort)]
    function_func.restype = ctypes.c_int

    h = 3
    w = 5

    ArrayType = ctypes.c_ushort * (h * w)  # Dynamically declare the array type: `unsigned short[15]` in our case
    array = ArrayType()  # The array type instance

    print_array(array, h, w)
    res = function_func(w, h, ctypes.cast(array, ctypes.POINTER(ctypes.c_ushort)))
    print("{:} returned: {:d}".format(function_func.__name__, res))

    print_array(array, h, w)


if __name__ == "__main__":
    print("Python {:s} on {:s}\n".format(sys.version, sys.platform))
    main()

输出:

[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q054753828]> ls
code.py  dll.c
[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q054753828]> gcc -fPIC -shared -o dll.so dll.c
[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q054753828]> ls
code.py  dll.c  dll.so
[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q054753828]> python3 code.py
Python 3.6.4 (default, Jan  7 2018, 15:53:53)
[GCC 6.4.0] on cygwin

 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
function returned: 15
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15

这篇关于从Python(ctypes)到C的指针以保存函数输出的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！