用Cython - 将字符串转换为char名单** [英] Cython - converting list of strings to char **

问题描述

我怎么能Python字符串的Python列表转换为空值终止的char ** 这样我就可以把它传递给外部的C函数？

How can I convert a python list of python strings to a null-terminated char** so I can pass it to external C function?

我有：

struct saferun_task:
    saferun_jail   *jail
    saferun_limits *limits

    char **argv
    int stdin_fd  
    int stdout_fd
    int stderr_fd

int saferun_run(saferun_inst *inst, saferun_task *task, saferun_stat *stat)

在CDEF的extern块

in cdef extern block

我想转换像（'./ a.out的'，'参数1'，'参数2'）
的东西，我可以分配给 saferun_task.argv

如何？

推荐答案

从用Cython文档：

From the Cython docs:

char* PyString_AsString (PyObject *string)

返回的字符串的内容一个空结束的重新presentation。该
指针指向字符串的内部缓冲区，而不是一个副本。数据
不能以任何方式被修改。它一定不能被解除分配

Returns a null-terminated representation of the contents of string. The pointer refers to the internal buffer of string, not a copy. The data must not be modified in any way. It must not be de-allocated.

我没有用Cython编译器的设置和方便的自动柜员机（我可以在以后运行，并核对），但是，这应该会导致code，看起来是这样的：

I don't have a Cython compiler setup and handy atm (I can run this later and check) but, this should results in code that looks something like:

from libc.stdlib cimport malloc, free

cdef char **string_buf = malloc(len(pystr_list) * sizeof(char*))

for i in range(len(pystr_list)):
    string_buf[i] = PyString_AsString(pystr_list[i])

# Do stuff with string_buf as a char**
# ...

free(string_buf)

现在的指针的StringBuf是char **你的原始数据而不复制任何条件 - 虽然你不应该在每个字符串编辑数据作为字符串应该为const char *进行处理（从文档）。如果你需要操作字符串，你将不得不memcpy的数据，或使你不关心在Python捣毁新对象 - 尽管因为你有一个字符串的元组，我怀疑你编辑它们。

The pointer stringBuf is now a char ** to your original data without copying any strings -- though you shouldn't edit the data in each string as the strings should be treated as const char* (from docs). If you need to manipulate the strings you will have to memcpy the data or make new objects which you don't care about trashing in Python -- though since you have a tuple of strings I doubt you are editing them.

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