Python ctypes:传递字符串数组 [英] Python ctypes: Passing an array of strings

问题描述

我在Python 2.7中有一个字符串数组，我想通过 ctypes 传递给C函数:

I have an array of strings in Python 2.7, which I would like to pass to a C function via ctypes:

unsigned int SetParams(unsigned int count, const char **params)

所以我可以在python中定义参数:

So I can define the parameters in python:

import ctypes as ct
lib = ct.cdll.LoadLibrary('...')
lib.SetParams.restype  = ct.c_uint
lib.SetParams.argtypes = [ct.c_uint, ct.POINTER(ct.c_char_p)]

但是现在当我想在上面的库调用中使用Python函数中的一组参数时，我实际上该如何调用它呢?我在想这样的事情:

but now when I am given a set of params in a Python function, which I would like to use in the above library call, how do I actually call it? I am thinking something like this:

def setParameters(strParamList):
    numParams    = len(strParamList)
    strArrayType = ct.c_char_p * numParams
    strArray     = strArrayType()
    for i, param in enumerate(strParamList):
        strArray[i] = param
    lib.SetParams(numParams, strArray)

我只是从 ctypes 开始，想知道是否有更自动化的方法来做到这一点?另外，赋值 strArray [i] = param 是否实际上在重新分配?如果是这样，这似乎很昂贵-是否有办法仅将字符串指针指向Python分配的缓冲区，或者它们不是NULL终止的?

I am just starting with ctypes and wondering if there is a more automated way to do this? Also is the assignment strArray[i] = param actually reallocating? If so, this seems quite expensive -- is there a way to do this just pointing the string pointers to Python-allocated buffers, or they are not NULL-terminated?

更新我确实浏览了几个相关的问题，但是找不到直接的问题来解决相同的问题.非常感谢

UPDATE I did look through a couple related questions, but could not find a direct one to deal with the same issues. Thank you very much

推荐答案

您认为正确.该代码有效.致电，例如:

You think correctly. That code works. Call with, for example:

setParameters(['abc','def','ghi'])

我没有查看源代码，但是Python 2.7(32位)上的 ctypes 确实通过了内部Python缓冲区(通过在C函数中修改传递的字符串并在输出之后打印它来进行测试)(在Python中称为调用")，这就是为什么您应该只将上述Python字符串传递给采用 const char * 的函数，或者至少已知不修改该字符串的原因.由于Python字符串是不可变的，因此在C语言下对它们的写入是不可取的.使用 ctypes.create_string_buffer 创建可写字符串，以传递给非常量 char * .

I haven't looked at the source, but ctypes on Python 2.7 (32-bit) does pass the internal Python buffer (tested by modifying the passed string in the C function and printing it after the call in Python), which is why you should only pass Python strings as above to functions that take const char* or at least are known not to modify the string. Since Python strings are immutable writing to them under C is a no-no. Use ctypes.create_string_buffer to create a writable string to pass to non-const char*.

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