python - ctypes:公开 C 中 malloc 的结构数组

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，但是 struct Arr 中 len_a 的输出与 C 中的设置不同。我的问题是:在 python 中将 Parse.arr 设置为 Arr 对象数组(最初是在 C 中分配/设置)的正确方法是什么？ pylink.py 中的 self.arr = cast(byref(self.parse.arr),POINTER(Arr*n)).contents 行明显不正确.

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

通过替换 pylink.py 中的这一行解决了这个问题

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在这里无效。我的实现与问题中链接的实现之间的一个重要区别是结构数组的声明方式。我的是一个指针，而另一个使用零大小的数组。欲了解更多信息，请参阅:https://docs.python.org/3/library/ctypes.html#ctypes.byref