Python-ctypes-如何调用函数和访问结构字段

Python - ctypes - How to call functions and access struct fields?

本文关键字：函数 访问 结构 字段 调用 何调用 Python-ctypes-      更新时间：2023-10-16

我有一个C库：

smart_string.h：

typedef struct SmartString {
    unsigned string_len;
    unsigned alloc_len;
    char *str;
    char *str_terminator;
} SmartString;
SmartString *SmartString_new(char *str);
... definitions of more functions ...

该实现位于名为smart_string.c.的文件中

我需要一个运行SmartString_new()函数和访问返回结构指针的字段的指南。

谁能教我怎么做吗？

谢谢！

回答自己并与您分享知识：

首先，需要从C文件创建一个共享库：

gcc -shared -fpic smart_string.c -o SmartString.so

然后，使用以下Python代码（有关每个已完成操作的解释，请参见注释）：

注意：上面API中显示的char*是C可编辑字符串，而const char*是只读字符串。由于C API需要char*而不是const char*，因此我们必须向其传递一个可变字符串，以便C代码可以对其进行编辑。默认情况下，Python字符串是不可变的。因此，我们在这里使用create_string_buffer()函数

python_smart_string.py：

import ctypes
from ctypes import *
# Defining the python type that represents the C SmartString
# It must extend the 'Structure' class
# Structure, c_uint, c_char_p, etc. were imported from ctypes
class SmartString(Structure):
    _fields_=[("string_len",c_uint),
              ("alloc_len",c_uint),
              ("str",c_char_p),
              ("str_terminator", c_char_p)]

# Loading the C shared lib I've just compiled
smartstring_lib = ctypes.CDLL('SmartString.so')
# Defining pointer to the SmartString_new() function
SmartString_new = smartstring_lib.SmartString_new
# Declaring the function return type - a pointer to a SmartString object - just like in the C code
SmartString_new.restype = POINTER(SmartString)
# Declaring list of parameter types. In this case, the list contains only one item,
# as the function has only one parameter
SmartString_new.argtypes = [c_char_p]
# Calling the SmartString_new() function. Expecting to get a pointer to SmartString object into 'my_str'
# The API requires a MUTABLE string, so create_string_buffer() is used here
# The reference to this string is not saved, as I don't care if it is modified by the C code
my_str = SmartString_new(create_string_buffer('my nice string'))
# Printing fields of the dereferenced returned value (dereferencing is done using '.contents')
print my_str.contents.string_len
print my_str.contents.alloc_len
print my_str.contents.str
print my_str.contents.str_terminator
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