python调用c语言代码

原本的机器学习项目都用python写好，老板这边又出了个新需求，将部分核心代码抽出来，用C编写，然后通过dll的方式引用，目的就是为了隐藏部分核心代码。

1. 编写C代码

使用codeblocks建dll库

  1. 选择ddl

image-20211228161228492

  1. main.c编写要导出的函数
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#include "main.h"
#include <stdio.h>

int DLL_EXPORT add_int(int a, int b)
{
    return a+b;
}

double* DLL_EXPORT Kernel( double* x,  double* y,  int row, int col,double gamma, double* w)
{
     double *res = NULL;
     res =(double*) malloc(sizeof(double)*row*col);
printf("%d %d\n",row,col); // c 数组空间创建
    for (int i = 0; i < row; i++) {
        for (int j = 0; j < col; j++) {
            res[i*col + j] = x[i*col + j] + y[i*col + j]; // 访问二维指针数组
        }
    }
    return res;
}
  1. main.h 编写导出头文件（默认）
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#ifndef __MAIN_H__
#define __MAIN_H__

#include <windows.h>

/*  To use this exported function of dll, include this header
 *  in your project.
 */

#ifdef BUILD_DLL
    #define DLL_EXPORT __declspec(dllexport)
#else
    #define DLL_EXPORT __declspec(dllimport)
#endif


#ifdef __cplusplus
extern "C"
{
#endif
// 这边编写导出的函数名称
int DLL_EXPORT add_int(int,int);
double* DLL_EXPORT Kernel(double*,double*,int,int,double,double*);

#ifdef __cplusplus
}
#endif

#endif // __MAIN_H__
  1. 编译
    编译成功后在对应文件夹bin/Debug生成dll文件

2 C调用dl

  1. 新建Console Application

  2. main.c代码编写

注意点：

  • 导入头文件”windows.h”
  • 函数定义 typedef int (*addInt)(int,int);
  • 导入DLL: HMODULE LoadLibrary
  • 获得dll的函数：add_int = (addInt)GetProcAddress(hDll, “add_int”);
  • FreeLibrary
  • 若c参数为二维指针，需要两次malloc
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#include <stdio.h>
#include <stdlib.h>
#include "windows.h"
typedef int (*addInt)(int,int);
typedef float** (*myKernel)(float**,float**,int,int,float,float*);
addInt add_int;
myKernel kernel;

int main()
{
    //asm("int3");
    HMODULE hDll = LoadLibrary("dll路径");
    if (hDll != NULL) {
        printf("Hello world!\n");
        add_int = (addInt)GetProcAddress(hDll, "add_int");
        int res_add = add_int(3,3);
        printf("%d\n",res_add);

        kernel = (myKernel)GetProcAddress(hDll,"Kernel");

        float arr1[2][3]={{1.1,2.0,3.0},{1.1,2,3.0}};
        float arr2[2][3]={{1,2,3},{1,2,3}};
        float (*temp1)[3] = arr1;
        float (*temp2)[3] = arr2;

        float **x = NULL;
     x = (float**)malloc(sizeof(float*)*2);

      for (int i = 0; i < 2; i++) {
            x[i]=(float*)malloc(3*sizeof(float));

        }

      for (int i = 0; i < 2; i++) {
            for (int j = 0; j < 3; j++) {
                  *(*(x+i)+j) = 5;
            }
        }


        float arr3[3] ={1,1,1};
        float *w = arr3;
        float** res = kernel(x,x,2,3,0.2,w);

        for (int i = 0; i < 2; i++) {
            for (int j = 0; j < 3; j++) {
                printf("%d %d %f\n ", i,j,*(*(res+i)+j));
            }
        }

    }
    FreeLibrary(hDll);
    return 0;
}

3 Python调用Dll

  1. 下载与导入ctypes包
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from ctypes import cdll,c_float,c_int
import numpy.ctypeslib as npct
import numpy as np
import win32api

  1. 导入dll

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    mykernel = cdll.LoadLibrary('dll路径')

  2. 要调用的C函数参数(argtypes)与返回值(restype)都有二维指针，因此需要预先设置

    npct.ndpointer表示是指针

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    mykernel.Kernel.argtypes = [npct.ndpointer(dtype=np.float64,ndim=2,shape = (2, 3),flags='C_CONTIGUOUS'),
                               npct.ndpointer(dtype=np.float64,ndim=2,shape = (2, 3),flags='C_CONTIGUOUS'),
                               c_int,
                               c_int,
                               c_float,
                               npct.ndpointer(dtype=np.float64,ndim=1,flags='C_CONTIGUOUS')]
        mykernel.Kernel.restype = npct.ndpointer(dtype=np.float64,ndim=2,shape = (2, 3),flags='C_CONTIGUOUS')

  3. numpy数组

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x=[[1,2,3],[4,5,6]]
   x=np.array(x,dtype=np.float64)
   w=[1,1,1]
   w=np.array(w,dtype=np.float64)
  
   print('addreess',k)
  1. 调用函数
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res = mykernel.Kernel(x,x,x.shape[0],x.shape[1],c_float(0.1),w)
# res就是返回的二维数组numpy
  1. Free
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win32api.FreeLibrary(mykernel._handle)

一个大坑：

python的float32要对应C的float类型，float64对应 double类型，否则会造成地址访问冲突
具体报错：exception: access violation reading 0xFFFFFFFFFFFFFFFF

参考

使用ctypes调用C函数库加速Numpy运算

Codeblocks上dll的创建和使用

Python如何调用DLL函数：C数组与numpy数组传递

Ctypes和NumPy