将tripple指针数组转换为numpy数组或列表python

时间:2016-09-26 20:53:01

标签: python c arrays python-3.x ctypes

我通过将c代码集成到我的python程序中来加速我的程序。我正在使用ctypes从python执行c中的函数。

c程序:

    #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#define MAX_ITERATIONS 1000

static void calculate_pixel(int x, int y, int size, float*** img){
    int i = 0;
    float a = 0.0, b = 0.0;

    while(a*a+b*b <= 4.0 && i < MAX_ITERATIONS){
        float temp_a = a;
        a = a*a - b*b + x;
        b = 2*a*b + y;

        i++;
    }

    float temp[3];
    memset(&temp, 0, sizeof(float)*3);

    if(i != MAX_ITERATIONS){
        float brightness = logf(1.75 + i - logf(log(a*a + b*b))) / log(MAX_ITERATIONS);
        temp[0] = brightness;
        temp[1] = brightness;
        temp[2] = 1;
    }

    memcpy(img[x][y], &temp, sizeof(float)*3);
} 

float*** mandel(int size){
    ssize_t len = (size)*sizeof(float*);
    float*** img = malloc(len);

    int x, y;
    for(x = 0; x < size; x++){
        img[x] = malloc(len);
        for(y = 0; y < size; y++){
            img[x][y] = malloc(sizeof(float)*3);
            calculate_pixel(x, y, size, img);
        }
    }

    return img;
}

Python程序:

 from ctypes import *
 import matplotlib.pyplot as pl

 size = 1000
 lib = './mandelbrot3.so'

 dll = cdll.LoadLibrary(lib)
 dll.mandel.argtypes = [c_int]

 #what i get in return from the c program
 dll.mandel.restype = POINTER(POINTER(POINTER(c_float*3)*size)*size)

 #calling function "mandel" in c program
 res = dll.mandel(size)

 #printing first value, does work this way
 print(res.contains[0].contains[0].contains[0])

 #creating a picture with pyplot, and inserting the array this way,
 #does not work because its pointers
 pl.imshow(res.contains)
 pl.show()

dll.mandel.restype是一个三脚指针,大小为:1000 * 1000 * 3。这将创建一个图片,其中大小为1000 * 1000像素,3个浮点数是rgb值。

所以我的问题是我从c程序返回的只是一个指针。我需要能够将其转换为普通的3D python列表或numpy数组。有没有比使用for循环读取指针数组中的所有元素并将它们插入新列表或numpy数组更好的方法呢?

1 个答案:

答案 0 :(得分:0)

我不确定这个三指针业务,但从C到numpy的数组是这样的:

假设您已向图片缓冲区收到ctypes POINTER,并且您知道heightwidth和数据类型......

您可以将ctypes数组与缓冲区中的图像大小相同,如下所示:

arr = (c_float * height * width * 3).from_address(addressof(data.contents))

在这种情况下,dataPOINTER

然后使用ndarray kwarg:

从中创建buffer
import numpy as np
img = np.ndarray(buffer=arr, dtype=np.float32, shape=(height, width, 3))