使用ctypes的回调函数 [英] Callback functions using ctypes

问题描述

我在C语言中有代码：

typedef result function_callback(struct mes_t* message, void* data) 
struct mes_t
{
uint32_t field1
uint32_t field2
void* data
};
function_one(&function_callback, data)

应用程序调用用户定义的 function_one ）回调函数 function_callback 。
在传递的回调函数中使用field1，field2和data参数（数据通常等于0）

The application calls the user-defined (in the function_one) callback function function_callback. In the callback function passed field1, field2 and data parameters (data is usually equal to 0)

此示例中python上的代码是否正确编写？

Whether the code on a python for this example is correctly written?

class mes_t(ctypes.Structure):
    pass
mes_t._fields_ = [
    ('field1', ctypes.c_uint32),
    ('dfield2', ctypes.c_uint32),
    ('data', ctypes.POINTER(ctypes.c_void_p))]
data_t=ctypes.c_void_p
data=data_t()
CALLBACK=CFUNCTYPE(ccg_msg, data_t)
cb_func=CALLBACK()
result = function_one(ctypes.byref(cb_func), ctypes.byref(data))

推荐答案

我猜这里解释代码的正确方法。调整后的示例代码段如下：

I've guessed here the right way to interpret your code. Adjusted sample snippets here:

typedef int /* or whatever */ result;

struct mes_t
{
    uint32_t field1;
    uint32_t field2;
    void* data;
};
typedef result function_callback(struct mes_t* message, void* data);
result function_one(function_callback fcb, void* data);

这是一些使用 function_one（）的ctypes Python示例。 code>：

And here's some example ctypes Python for making use of function_one():

class mes_t(ctypes.Structure):
    _fields_ = (
        ('field1', ctypes.c_uint32),
        ('field2', ctypes.c_uint32),
        ('data', ctypes.c_void_p))

result_t = ctypes.c_int; # or whatever

callback_type = ctypes.CFUNCTYPE(result_t, ctypes.POINTER(mes_t), ctypes.c_void_p)
function_one.argtypes = (callback_type, ctypes.c_void_p)
function_one.restype = result_t

data_p = ctypes.c_char_p('whatever')

def the_callback(mes_p, data_p):
    my_mes = mes_p[0]
    my_data_p = ctypes.cast(data_p, ctypes.c_char_p)  # or whatever
    my_data = my_data_p.value
    print "I got a mes_t object! mes.field1=%r, mes.field2=%r, mes.data=%r, data=%r" \
          % (my_mes.field1, my_mes.field2, my_mes.data, my_data)
    return my_mes.field1

result = function_one(callback_type(the_callback), ctypes.cast(data_p, ctypes.c_void_p))

您将看到此代码与您的代码之间存在许多差异；可能太多，无法对所有内容进行全面说明。但是，如果有一些看起来特别令人困惑的部分，我可以解释一些特定的部分。但是，总的来说，对ctypes指针的工作方式有一个很好的了解是很重要的（例如，您可能不希望有一个指向void的指针，但这就是您的python代码所做的事情。）

You'll see there are numerous differences between this and your code; probably too much to give full explanations of everything. I can, however, explain a few particular parts if there are some which seem especially confusing. In general, though, it's important to have a good understanding of how ctypes pointers work (for example, you probably don't want a pointer to a pointer to void, but that's what your python code did).

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