在python中如何设置LP_c_ubyte的值 [英] In python how do I set the value of a LP_c_ubyte

问题描述

我正在使用python ctypes为C DLL创建Python包装器。我无法使用python更新指向内存中值的指针。

I am creating a Python wrapper for a C DLL using python ctypes. I am having trouble updating a pointer to value in memory with python.

在此示例中，我有一个具有注册回调函数的DLL。调用回调函数将创建无符号char变量，将指向该变量的指针传递给回调函数，然后输出该变量的更新值。

In this example I have a DLL that has a register callback function. A invoke callback function that creates unsigned char variable, passes a pointer to that variable to the callback function, then prints the updated value of that variable.

我希望发生的是python函数 callbackUpdateValue 将更新的值foo ，更新后的值将打印在C DLL DoCallBack 函数中。将打印 0 的值，而不是预期的 99

What I expected to happen is that the python function callbackUpdateValue would update the value of foo, and the updated value would be printed in C DLL DoCallBack function. The value of 0 is printed instead of the expected value of 99

我的问题是：在python中，如何在 callbackUpdateValue foo 的值$ c>以便可以将其打印在C DLL DoCallBack 函数中？

My question is: In python how do I update the value of foo in callbackUpdateValue so that it can be printed in the C DLL DoCallBack function?

我已将代码最小化为

DLL C ++代码

DLL具有两个功能。一个注册一个回调，另一个调用回调并打印结果。

The DLL has two functions. One to register up a callback, the other to invoke the callback and print the results.

#include <stdio.h>
typedef void(*FPCallback)(unsigned char * foo);
FPCallback g_Callback;

extern "C" __declspec( dllexport ) void RegisterCallback(void(*p_Callback)(unsigned char * foo)) {
    g_Callback = p_Callback ; 
}

extern "C" __declspec( dllexport ) void DoCallBack() {
    unsigned char foo = 0 ; 
    g_Callback( &foo ); 
    printf( "foo=%d\n", foo); 
}

Python代码

Python代码设置了回调函数，然后从DLL调用DoCallBack函数。

The python code sets up the call back function, then calls the DoCallBack function from the DLL.

from ctypes import *

def callbackUpdateValue( foo ):
    foo = 99 

customDLL = cdll.LoadLibrary ("customeDLL.dll")

# RegisterCallback
CustomDLLCallbackFUNC = CFUNCTYPE(None, POINTER( c_ubyte))
CustomDLLCallback_func = CustomDLLCallbackFUNC( callbackUpdateValue )
RegisterCallback = customDLL.RegisterCallback
RegisterCallback.argtypes = [ CustomDLLCallbackFUNC ]
RegisterCallback( CustomDLLCallback_func ) 

# DoCallBack
DoCallBack = customDLL.DoCallBack

# Call the callback 
DoCallBack() 

推荐答案

定义python回调的正确方法是

The correct way to define the python callback is

def callbackUpdateValue( foo ):
    foo[0] = 99

其中 foo [0] 取消引用指针。可在此处找到更多信息： https://docs.python.org /2.5/lib/ctypes-callback-functions.html

where foo[0] dereferences the pointer. More info can be found here: https://docs.python.org/2.5/lib/ctypes-callback-functions.html

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