ctypes的运用（把一个numpy数组传入c中）

1.把一个二维数组转化成一维的，传入C

void show_matrix(int *matrix, int rows, int columns)
{
    int i, j;
    for (i=0; i

 编译成动态库供python调用 ，gcc -shared -O2 mystuff.c  -ldl -o mystuff.so

import ctypes
import numpy as np
 
lib = ctypes.cdll.LoadLibrary("./mystuff.so")
arr = np.zeros((3,5))
#arr = np.array([[1,2],[3,4]])
tmp = np.asarray(arr)
rows, cols = tmp.shape
dataptr = tmp.ctypes.data_as(ctypes.c_char_p)
lib.show_matrix(dataptr, rows, cols)

运行 python test.py

2把numpy的二维数组打包成ctypes的标准数组形式，传送给C。


from ctypes import *
import numpy
 
def Convert1DToCArray(TYPE, ary):
    arow = TYPE(*ary.tolist())
    return arow
 
def Convert2DToCArray(ary):
    ROW = c_int * len(ary[0])
    rows = []
    for i in range(len(ary)):
        rows.append(Convert1DToCArray(ROW, ary[i]))
    MATRIX = ROW * len(ary)
    return MATRIX(*rows)
 
a=numpy.array([[1,2,2],[1,3,4]])
caa = Convert2DToCArray(a)
 
def ShowCArrayArray(caa):
    for row in caa:
        for col in row:
            print col
ShowCArrayArray(caa)

3  如果将python中list传入C函数数组，则需要提前转换。

import ctypes
pyarray = [1, 2, 3, 4, 5]
carray = (ctypes.c_int * len(pyarray))(*pyarray) //有点类似malloc的方式生成carray
print so.sum_array(carray, len(pyarray))

如果如果需要将C array返回python，需要提前把array传入，然后在C函数中修改，返回时再把c array转换为np.array

pyarray = [1,2,3,4,5,6,7,8]
carray = (ctypes.c_int*len(pyarray))(*pyarray)
so.modify_array(carray, len(pyarray))
print np.array(carray)

output

[10 20 30 40 50 60 70 80]

也可以用形参方式提前定义函数接口，然后再传入numpy结构

import ctypes
import numpy as np
from numpy.ctypeslib import ndpointer
so = ctypes.CDLL('./sum.so')
pyarray = np.array([1,2,3,4,5,6,7,8], dtype="int32")
fun = so.modify_array
fun.argtypes = [ndpointer(ctypes.c_int), ctypes.c_int]
fun.restype = None
fun(pyarray, len(pyarray))
print np.array(pyarray)

注意：numpy中的数据类型指定很重要，即dtype的设定