python - 将带有数组的嵌套 ctypes 结构传递给 C 库函数不符合预期

Question

我有以下 C 代码，我将从 python 脚本中使用它。

这只是自动生成的巨大库的摘录，不幸的是我无法更改它。在这里，我只是想将结构元素打印到控制台来演示出了什么问题。

// CFunc.h
#include <stdio.h>

typedef struct
{
    int npar;
    struct
    {
        int id;
        int value;
    } params[10];
} Data_t;

void Cfunc( const Data_t * d);


// CFunc.c

#include "CFunc.h"

void Cfunc( const Data_t * d)
{
    int inpar = 0;
    int maxnpar = 0;

    printf("%d:\n", d->npar);
    maxnpar = d->npar;

    inpar=0;
    while (maxnpar > inpar)
    {
        printf("  %d: %08x %08x\n", inpar, d->params[inpar].id, *(int*)&d->params[inpar].value);
        inpar++;
    }
}

它被编译并链接到共享库:

gcc -fPIC -c CFunc.c -o CFunc.o
gcc -shared -lrt -Wl,-soname,libCFunc.so.1 -o libCFunc.so CFunc.o

所以我使用 ctypes 进行了以下实现:

from ctypes import *

lib = CDLL('./libCFunc.so')


class Data_2(Structure):
    pass
class Data_t(Structure):
    def __init__(self, list):
        self.npar = len(list)
        self.params = (Data_2 * self.npar)(*list)

Data_2._fields_ = [
    ('id', c_int),
    ('value', c_int),
]
Data_t._fields_ = [
    ('npar', c_int),
    ('params', POINTER(Data_2)),
]

def pyFunc(d):
    lib.Cfunc.argtypes = (POINTER(Data_t),)

    lib.Cfunc(byref(d))

    return

因此，我从给定元组列表中初始化该结构，在本例中只有 2 个元组，并调用 C 函数来查看其输出。

paramlist = ( 
    ( 0x050000000, 0x00000000 ),  
    ( 0x050000001, 0x447a0000 ) )
temp = Data_t(paramlist)

pyFunc(temp)

不幸的是，输出不符合预期:

2:
0: 00000000 79948ef0
1: 00007fe5 00000000

有什么想法我错过了什么吗？

Answer 1

[Python 3]: ctypes - A foreign function library for Python .

• C 和 Python 的结构不匹配
  • params是数组而不是指针
• 由于上述不一致，您使 Python 中的事情变得过于复杂:
  • 您没有不完整的类型，因此您的结构可以静态定义

我稍微重组了你的代码。

dll.h:

#pragma once


typedef struct Data_ {
    int npar;
    struct
    {
        int id;
        int value;
    } params[10];
} Data;


void test(const Data *d);

dll.c:

#include "dll.h"
#include <stdio.h>


void test(const Data *d) {
    int inpar = 0;
    int maxnpar = 0;

    printf("%d:\n", d->npar);
    maxnpar = d->npar;

    inpar = 0;
    while (inpar < maxnpar)
    {
        printf("  %d: %08x %08x\n", inpar, d->params[inpar].id, *(int*)&d->params[inpar].value);
        inpar++;
    }
}

code.py:

#!/usr/bin/env python3

import sys
import ctypes


DLL = "./libdll.so"


class DataInner(ctypes.Structure):
    _fields_ = [
        ("id", ctypes.c_int),
        ("value", ctypes.c_int),
    ]


DataInnerArr10 = DataInner * 10


class Data(ctypes.Structure):
    _fields_ = [
        ("npar", ctypes.c_int),
        ("params", DataInnerArr10),
    ]

    def __init__(self, data):
        self.npar = len(data)
        self.params = DataInnerArr10(*data)


def main():
    dll_dll = ctypes.CDLL(DLL)
    test_func = dll_dll.test
    test_func.argtypes = [ctypes.POINTER(Data)]

    param_list = (
        (0x050000000, 0x00000000),
        (0x050000001, 0x447a0000),
    )

    d = Data(param_list)

    test_func(ctypes.byref(d))
    print("Done.")


if __name__ == "__main__":
    print("Python {:s} on {:s}\n".format(sys.version, sys.platform))
    main()

输出:

[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q054888242]> ls
code.py  dll.c  dll.h
[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q054888242]> gcc -shared -fPIC -o libdll.so dll.c
[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q054888242]> ls
code.py  dll.c  dll.h  libdll.so
[cfati@cfati-5510-0:/cygdrive/e/Work/Dev/StackOverflow/q054888242]> python3 code.py
Python 3.6.4 (default, Jan  7 2018, 15:53:53)
[GCC 6.4.0] on cygwin

2:
  0: 50000000 00000000
  1: 50000001 447a0000
Done.