ctypes包含数组的结构 [英] ctypes struct containing arrays
问题描述
我正在尝试使用 ctypes
。我对处理包含数组的C结构感兴趣。考虑以下 my_library.c
I'm trying to use ctypes
. I'm interested in manipulating C structs containing arrays. Consider the following my_library.c
#include <stdio.h>
typedef struct {
double first_array[10];
double second_array[10];
} ArrayStruct;
void print_array_struct(ArrayStruct array_struct){
for (int i = 0; i < 10; i++){
printf("%f\n",array_struct.first_array[i]);
}
}
,假设我已经编译了它在共享库 my_so_object.so
中,可以使用Python
and suppose I've compiled it in a shared library my_so_object.so
From Python I can do something like this
import ctypes
from ctypes import *
myLib = CDLL("c/bin/my_so_object.so")
class ArrayStruct(ctypes.Structure):
_fields_ = [('first_array', ctypes.c_int * 10), ('second_array', ctypes.c_int * 10)]
def __repr__(self):
return 'ciaone'
myLib.print_array_struct.restype = None
myLib.print_array_struct.argtype = ArrayStruct
my_array_type = ctypes.c_int * 10
x1 = my_array_type()
x2 = my_array_type()
a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
x1[0:9] = a[0:9]
a = [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
x2[0:9] = a[0:9]
print(my_array_type)
>>> <class '__main__.c_int_Array_10'>
print(x1[2])
>>> 3
print(x2[2])
>>> 13
x = ArrayStruct(x1, x2)
print(x.first_array[0:9])
>>> [1, 2, 3, 4, 5, 6, 7, 8, 9]
到目前为止太好了:我已经创建了正确的类型,并且一切似乎都正常。但是然后:
So far so good: I've created the correct types and everything seems working fine. But then:
myLib.print_array_struct(x)
>>> 0.000000
>>> 0.000000
>>> 0.000000
>>> 0.000000
>>> 0.000000
>>> 0.000000
>>> 0.000000
>>> 0.000000
>>> 0.000000
>>> 0.000000
我显然错过了一些东西。可以识别 ArrayStruct
类型(否则,调用 myLib.print_array_struct(x)
会引发错误)但未正确初始化。
I'm clearly missing something. The ArrayStruct
type is recognized (otherwise the call myLib.print_array_struct(x)
would throw an error) but not correctly initialized.
推荐答案
代码有2个问题(如我在评论中所述):
There were 2 problems with the code (as I stated in the comment):
- print_array_struct.argtype -这是不正确的
- 在 C 中,数组是基于 double ,而在 Python 中它们基于 ctypes.c_int ( int )
- print_array_struct.argtype - which is incorrect
- In C the arrays are double based, while in Python they are ctypes.c_int (int) based
有关更多详细信息,请检查 [Python 3.Docs]:ctypes-Python的外部函数库。
我修改了您的 Python 代码,以纠正上述错误(以及其他一些小错误)。
For more details, check [Python 3.Docs]: ctypes - A foreign function library for Python.
I modified your Python code, to correct the above mistakes (and some other minor stuff).
code00.py :
#!/usr/bin/env python3
import sys
import ctypes
DLL_NAME = "./my_so_object.so"
DOUBLE_10 = ctypes.c_double * 10
class ArrayStruct(ctypes.Structure):
_fields_ = [
("first_array", DOUBLE_10),
("second_array", DOUBLE_10),
]
def main():
dll_handle = ctypes.CDLL(DLL_NAME)
print_array_struct_func = dll_handle.print_array_struct
print_array_struct_func.argtypes = [ArrayStruct]
print_array_struct_func.restype = None
x1 = DOUBLE_10()
x2 = DOUBLE_10()
x1[:] = range(1, 11)
x2[:] = range(11, 21)
print([item for item in x1])
print([item for item in x2])
arg = ArrayStruct(x1, x2)
print_array_struct_func(arg)
if __name__ == "__main__":
print("Python {:s} on {:s}\n".format(sys.version, sys.platform))
main()
输出:
[cfati@cfati-ubtu16x64-0:~/Work/Dev/StackOverflow/q050447199]> python3 code00.py
Python 3.5.2 (default, Nov 23 2017, 16:37:01)
[GCC 5.4.0 20160609] on linux
[1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0]
[11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0]
1.000000
2.000000
3.000000
4.000000
5.000000
6.000000
7.000000
8.000000
9.000000
10.000000
错误 #1。 是(更新) [SO]:通过ctypes从Python调用的C函数返回错误值(@CristiFati的回答)。
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