Python ctypes 到 return 函数指针数组

Question

我正在使用一个包含单个调用的 .dll，其中 returns 一个函数指针数组。 GetMyApi() returns 一个指向结构的指针，它是一个函数指针数组。这些功能本身具有不同的输入和输出。到目前为止我尝试了什么：

我不能轻易修改的C代码：

C 代码：

typedef struct My_Api_V2
{
    int                 (__cdecl *IsValidInt)(int i);
    int                 (__cdecl *InvalidInt)();
    int                 (__cdecl *IsValidSize)(size_t i);
} my_Api_V2;

const my_Api_V2* GetMyApi(int version);   // This function is accessed from DLL

Python 努力：

from ctypes import *

my_dll = cdll.LoadLibrary(path_to_my_dll)
my_api = my_dll.GetMyApi
my_api.argtypes[c_int]  #version number
my_api.restypes = c_void_p

firstfuncptr = my_api(2)
firstfunc = prototype(firstfuncptr)
firstfunc.argtypes[c_int]
firstfunc.restypes = c_int

test = firstfunc(23)

此时，我只是想让函数列表中的第一个函数恢复工作。感谢任何帮助我指明更好方向的帮助。

Answer 1

事情并不像第一眼想象的那么简单。我要 post 一个虚拟示例，它恰好包含使用 .dlls (.sos)（如 [Python 3.Docs]: ctypes - A foreign function library for Python 中所述）。

dll00.c:

#include <stdio.h>

#if defined(_WIN32)
#  define DLL00_EXPORT __declspec(dllexport)
#  pragma warning(disable: 4477)  // !!! Just to avoid having additional code (macro for size_t), do NOT do this !!!
#else
#  define DLL00_EXPORT
#endif

#define PRINT_MSG_0() printf("        [%s] (%d) - [%s]\n", __FILE__, __LINE__, __FUNCTION__)
#define PRINT_MSG_1I(ARG0) printf("        [%s] (%d) - [%s]:  ARG0: %d\n", __FILE__, __LINE__, __FUNCTION__, ARG0)


static int IsValidInt(int i) {
    PRINT_MSG_1I(i);
    return -i;
}

static int InvalidInt() {
    PRINT_MSG_0();
    return 0;
}

static int IsValidSize (size_t i) {
    PRINT_MSG_1I(i);
    return -i;
}


typedef struct DllInterfaceV2Struct {
    int (__cdecl *IsValidIntFuncPtr)(int i);
    int (__cdecl *InvalidIntFuncPtr)();
    int (__cdecl *IsValidSizeFuncPtr)(size_t i);
} DllInterfaceV2;


static DllInterfaceV2 intfV2 = { IsValidInt, InvalidInt, IsValidSize };


#if defined(__cplusplus)
extern "C" {
#endif

DLL00_EXPORT const DllInterfaceV2 *GetInterfaceV2(int version);

#if defined(__cplusplus)
}
#endif


DLL_EXPORT const DllInterfaceV2 *GetInterfaceV2(int version) {
    if (version == 2) {
        return &intfV2;
    } else {
        return NULL;
    }
}

code00.py:

#!/usr/bin/env python3

import sys
import ctypes


DLL_NAME = "test00.dll"
DLL_FUNC_NAME = "GetInterfaceV2"

# "Define" the Python counterparts for C stuff in order to be able to use it

IsValidIntFuncPtr = ctypes.CFUNCTYPE(ctypes.c_int, ctypes.c_int)
InvalidIntFuncPtr = ctypes.CFUNCTYPE(ctypes.c_int)
IsValidSizeFuncPtr = ctypes.CFUNCTYPE(ctypes.c_int, ctypes.c_size_t)

class DllInterfaceV2(ctypes.Structure):
    _fields_ = [
        ("is_valid_int", IsValidIntFuncPtr),
        ("invalid_int", InvalidIntFuncPtr),
        ("is_valid_size", IsValidSizeFuncPtr)
    ]


# Now, play with C stuff

def test_interface_ptr(intf_ptr):
    print("Testing returned interface: {:}\n".format(intf_ptr))
    if not intf_ptr:
        print("    NULL pointer returned from C\n")
        return
    intf = intf_ptr.contents  # Dereference the pointer
    res = intf.is_valid_int(-2718281)
    print("    `is_valid_int` member returned: {:d}\n".format(res))
    res = intf.invalid_int()
    print("    `invalid_int` member returned: {:d}\n".format(res))
    res = intf.is_valid_size(3141592)
    print("    `is_valid_size` member returned: {:d}\n\n".format(res))


def main():
    test_dll = ctypes.CDLL(DLL_NAME)
    get_interface_v2_func = getattr(test_dll, DLL_FUNC_NAME)  # Or simpler: test_dll.GetInterfaceV2
    get_interface_v2_func.argtypes = [ctypes.c_int]
    get_interface_v2_func.restype = ctypes.POINTER(DllInterfaceV2)

    pintf0 = get_interface_v2_func(0)
    test_interface_ptr(pintf0)
    pintf2 = get_interface_v2_func(2)
    test_interface_ptr(pintf2)


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

备注:

C部分：
- 我不得不添加一些虚拟代码来测试和说明行为
- 虽然你提到它不可修改，但我改变了一些东西（主要是命名/编码风格，...）：
  - 两个字母大小写 + 下划线 都不好看（至少对我来说）
  - "my"（或其任何变体）在（函数、类或任何其他）名称中简直让我抓狂
Python部分：
- 正如我在评论中所述，C 内容必须是 Python 中的 "duplicated"
虽然我认为这是一个主要的设计缺陷，但为了尽可能接近问题，我只是照着做（GetInterfaceV2（V2 部分）考虑到它的 arg (version))
- 我个人的意见（尽管没有所有上下文）是（为了确保可伸缩性）函数应该 return 一个通用结构，带有一个附加字段（例如 version ) 可以由客户端应用程序检查。

输出:

(py35x64_test) e:\Work\Dev\Whosebug\q051507196>"c:\Install\x86\Microsoft\Visual Studio Community15\vc\vcvarsall.bat" x64

(py35x64_test) e:\Work\Dev\Whosebug\q051507196>dir /b
code00.py
dll00.c

(py35x64_test) e:\Work\Dev\Whosebug\q051507196>cl /nologo dll00.c  /link /DLL /OUT:test00.dll
dll00.c
   Creating library test00.lib and object test00.exp

(py35x64_test) e:\Work\Dev\Whosebug\q051507196>dir /b
code00.py
dll00.c
dll00.obj
test00.dll
test00.exp
test00.lib

(py35x64_test) e:\Work\Dev\Whosebug\q051507196>"e:\Work\Dev\VEnvs\py35x64_test\Scripts\python.exe" code00.py
Python 3.5.4 (v3.5.4:3f56838, Aug  8 2017, 02:17:05) [MSC v.1900 64 bit (AMD64)] on win32

Testing returned interface: <__main__.LP_DllInterfaceV2 object at 0x00000219984EBAC8>

   NULL pointer returned from C

Testing returned interface: <__main__.LP_DllInterfaceV2 object at 0x00000219984EBB48>

        [dll00.c] (16) - [IsValidInt]:  ARG0: -2718281
    `is_valid_int` member returned: 2718281

        [dll00.c] (22) - [InvalidInt]
    `invalid_int` member returned: 0

        [dll00.c] (28) - [IsValidSize]:  ARG0: 3141592
    `is_valid_size` member returned: -3141592

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