Question

看了这个问题：

ctypes: How do I define an array of a structure as a field of another structure?

现在我正在尝试实现我的解决方案版本，但len_a中struct Arr的输出与它在C中的设置不同。我的问题是：什么是正确的方法将Parse.arr设置为python中的Arr对象数组（最初在C中分配/设置）？ pylink.py 中的self.arr = cast(byref(self.parse.arr),POINTER(Arr*n)).contents行显然有误。

clink.c

#include <stdio.h>
#include <stdlib.h>
#define SIZE 10

struct Arr {
    int len_a;
};

struct Parse {
    struct Arr* arr;
    int len_arr;
};

struct Parse* C_new_domain(void) {
    int i = 0;
    struct Parse* parse = malloc(sizeof(struct Parse));   
    parse->arr = malloc(SIZE*sizeof(struct Arr));
    for (i=0 ; i<SIZE ; i++) {
        parse->arr[i].len_a = i;
    }
    parse->len_arr = SIZE;
    return parse;
}

void C_end_program(struct Parse* parse) {
    free(parse->arr);
    free(parse);
    return;
}

pylink.py

import sys
from ctypes import *
_lib = cdll.LoadLibrary('./libclink.so')

class Arr(Structure):
    def __init__(self, obj, name=""):
        self.obj = obj
    _fields_ = [("len_a", c_int)]


class Parse(Structure):
    def __init__(self, obj, name=""):
        self.obj = obj
    _fields_ = [("arr", POINTER(Arr)),
                ("len_arr", c_int)]

class Domain(object):
    domain = POINTER(Parse)
    parse = None
    arr = None
    _lib.C_new_domain.argtype = None
    _lib.C_new_domain.restype = POINTER(Parse)
    _lib.C_end_program.argtype = POINTER(Parse)
    def __init__(self):
        self.domain = _lib.C_new_domain()
        self.parse = self.domain.contents
        n = self.parse.len_arr
        self.arr = cast(byref(self.parse.arr),POINTER(Arr*n)).contents
    def end(self):
        _lib.C_end_program(self.domain)

if __name__ == '__main__':
    domain = Domain()
    for count, array in enumerate(domain.arr):
        print "[Hoping this is %d] --> array[%d].len_a is %d"%(count, count, array.len_a)
    domain.end()

输出

[Hoping this is 0] --> array[0].len_a is 25023216
[Hoping this is 1] --> array[1].len_a is 0
[Hoping this is 2] --> array[2].len_a is 10
[Hoping this is 3] --> array[3].len_a is 32512
[Hoping this is 4] --> array[4].len_a is 14962
[Hoping this is 5] --> array[5].len_a is 0
[Hoping this is 6] --> array[6].len_a is 33
[Hoping this is 7] --> array[7].len_a is 0
[Hoping this is 8] --> array[8].len_a is 10
[Hoping this is 9] --> array[9].len_a is 0

Answer 1

通过在 pylink.py

中替换此行来解决此问题

self.arr = cast(byref(self.parse.arr), POINTER(Arr*n)).contents

与

self.arr = cast(self.parse.arr, POINTER(Arr*n)).contents

属性arr被声明为POINTER(Arr)，因此函数byref在此无效。我的实现之间的一个重要区别是问题中链接的是如何声明结构数组。我是一个指针，而另一个使用零大小的数组。有关详细信息，请参阅：https://docs.python.org/3/library/ctypes.html#ctypes.byref

ctypes：暴露C中malloc的结构数组

1 个答案: