Python ctypes的byref和pointer区别

分手后的思念是犯贱 2022-02-18 11:39 282阅读 0赞

参考：[https://www.cnblogs.com/fendou-999/p/3527449.html?utm\_source=tuicool&utm\_medium=referral][https_www.cnblogs.com_fendou-999_p_3527449.html_utm_source_tuicool_utm_medium_referral]

byref(n)返回的相当于C的指针右值&n，本身没有被分配空间：

>>> from ctypes import \*  
>>> n = c\_int(0)  
>>> p = byref(n)  
>>> pp = byref(p)  
Traceback (most recent call last):  
  File "<pyshell\#4>", line 1, in <module>  
    pp = byref(p)  
TypeError: byref() argument must be a ctypes instance, not 'CArgObject'

pointer返回的相当于指针左值T\* p=&n，可以改变，可以取地址:

>>> from ctypes import \*  
>>> n = c\_int(0)

>>> q = pointer(n)  
>>> q.contents = c\_int(1)  
>>> qq = byref(q)  
>>> dir(qq)  
\['\_\_class\_\_', '\_\_delattr\_\_', '\_\_dir\_\_', '\_\_doc\_\_', '\_\_eq\_\_', '\_\_format\_\_', '\_\_ge\_\_', '\_\_getattribute\_\_', '\_\_gt\_\_', '\_\_hash\_\_', '\_\_init\_\_', '\_\_le\_\_', '\_\_lt\_\_', '\_\_ne\_\_', '\_\_new\_\_', '\_\_reduce\_\_', '\_\_reduce\_ex\_\_', '\_\_repr\_\_', '\_\_setattr\_\_', '\_\_sizeof\_\_', '\_\_str\_\_', '\_\_subclasshook\_\_', '\_obj'\]  
>>> type(qq)  
<class 'CArgObject'>                  \#'CArgObject'是什么对象？？？

>>> qq  
<cparam 'P' (010AD238)>  
>>> q  
<\_\_main\_\_.LP\_c\_long object at 0x010AD210>  
>>> q.contents  
c\_long(1)

对于T\*\*参数，通常你得构造一个pointer，然后byref传进去

以\_\_开头并以\_\_结束的属性（\_\_class\_\_、\_\_dir\_\_ 等）都是为内置方法（built-in method），唯独\_obj不是

>>> qq.\_obj  
<\_\_main\_\_.LP\_c\_long object at 0x010B8120>  
>>> q  
<\_\_main\_\_.LP\_c\_long object at 0x010B8120>

由以上执行代码可知，二维指针qq的\_obj属性就是该二维指针的首地址，即指向q指针的地址

PS: addressof返回一个Python整数，不能直接传给C那边

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