在 Python 中访问空指针(使用 SWIG 或其他东西) [英] Accessing void pointers in Python (using SWIG or something else)

问题描述

我一直在尝试使用 SWIG 来包装一个简单的库，该库使用 ioctl() 来填充如下所示的结构:

I've been trying to use SWIG to wrap around a simple library that uses ioctl() to populate a structure like the following:

struct data
{
  header* hdr;
  void* data;
  size_t len;
};

data 是指向缓冲区的指针，len 是该缓冲区的长度.

data is a pointer to a buffer, len is the length of that buffer.

我不知道如何将数据转换为 Python 字符串(或数组).此外，我需要一种方法来释放析构函数中的缓冲区.任何建议表示赞赏.

I'm unable to figure out how to convert data to a Python string (or array). Furthermore, I need a way to free that buffer in the destructor. Any suggestions are appreciated.

推荐答案

既然你在 Q 的标题中说了或者别的什么"——如果你选择使用 ctypes，你可以用 c_void_p 表示一个 void*(ctypes 的一种 基本数据类型, 并从 C 运行时库中访问诸如 free 和 memcpy 之类的函数(只要后者可用作 DLL/.so 动态库，但这种情况非常广泛)天).要获得一个可变字符缓冲区，您可以在其中 memcpy 数据，请使用 create_string_buffer.

Since you say "or something else" in the Q's title -- if you choose to use ctypes, you can represent a void* with c_void_p (one of ctypes' fundamental data types, and access functions such as free and memcpy from the C runtime library (as long as the latter's available as a DLL / .so dynamic library, but that's true pretty widely these days). To get a mutable character buffer into which you can memcpy the data, use create_string_buffer.

当然，您也可以使用 Python C API -- PyByteArray_FromStringAndSize 是你在这种情况下用来从你的 void* 和长度制作一个字节数组副本(当然你会在适当的时候直接调用 free，因为它只是 C 代码).

Of course you could alternatively use the Python C API -- PyByteArray_FromStringAndSize is what you'd use in this case to make a byte array copy from your void* and length (and of course you'd call free directly, when appropriate, since it's just C code anyway).

另一种可以考虑的可能性是 Cython，一种类似 Python 的语言，旨在编写 Python 扩展，并且Cython 编译器可以从 Cython 源代码生成可编译的 C 代码 - 在 Cython 中，您的 struct 将是:

Another possibility to consider is Cython, a Python-like language designed to write Python extensions and such that the Cython compiler can generate compilable C code from Cython sources - in Cython, your struct would be:

cdef struct data:
    void* hdr
    void* data
    unsigned int* len

假设您不想麻烦地声明 header(即，这里只有 data 和 len 对您很重要) -- size_t，我相信，现在不是 Cython 的一部分(我可能是错的，他们确实不断添加东西；-)，但是 unsigned int 可能可以做.

assuming you don't want to go to the trouble of declaring header (i.e., that only data and len matter to you here) -- size_t, I believe, is not part of Cython at this time (I could be wrong, they do keep adding stuff;-), but unsigned int can probably do.

抱歉，自从我认真使用 SWIG 已经太久了(所有这些优秀的替代品是什么)——如果不是标题中那个诱人的或其他"条款，我会跳过 Q；-).

Sorry, it's been too long since I used SWIG in earnest (what with all these excellent alternatives) -- I'd have skipped the Q were it not for that tempting "or something else" clause in the title;-).

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