c_void_p arguments in callbacks using ctypes in Python -


I am a frequent user of CTIPs, but I have to face the things I can not understand.

First of all, when I define a callback with c_void_p, callback will get an integer.

I have seen some other posts that wrap c_void_p by wrapping it in second digit when it returns the c_void_p return value. So, I thought I could try it for reasoning in callback definition: POINTER (c_void_p) When called callback, now I get a pointer, but I still do not know that this value indicates data is.

Since C_void_p indicates the buffer with the binary data, I do not believe that I can use a c_char_p I put the array without any realization, whose length is passed to me But then Python tells me that I have a tupe, and there is no "content" or "value" property which I can use.

Suggestion

In the callback, as an integer, c_void_p is normal. It's using simple type of getfunc to auto conversion - the same as receiving a c_void_p as the structure field . CTIP will not automatically transition for a simple type of subclass - e.g. Type ('my_void_p', (c_void_p,), {}) . Although I do not think there is a case in this matter.

Say that you have an integer address in p . You can * it by using c_char one of the length of the line n : 

  Buf = cast (p, pointer (c_char * n)) [0] # 2.6+ buf = (c_char * n) .from_address (p)   
 He said, knowing that I define callback to use the  four * , I use  POINTER (c_char) . Then access the buffer with an index or a piece, e.g.  P [0]  or  P [: n] .  
 
 *   p [n]  is equal to  * (p + n) , where  *  The operator is operator and also using the pointer arithmetic based on the size of the director. You can use  p [0]  instead of  p.contents , but call the same type  getfunc  converter, if applicable.

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