I have a c function that takes as arguments a void * pointer and an integer length for the size of the buffer pointed to.
e.g.
char* myfunc(void *mybuffer, int buflen)
On the python side I have a bytes object of binary data read from a file.
What I am trying to figure out is the right conversions to be able to call the c function from python, and am struggling a bit.
I understand the conversions for dealing with simple string data (e.g. encoding to utf-8 and using a char_p type) but dealing with a bytes object has been a bit of a struggle....
Thanks in advance!
Given your commented description, you can just use the obvious types if you don't need to free the returned char* memory. You can pass a bytes object to a void*. Here's a quick demo:
test.c
#include <stdio.h>
#include <stdint.h>
#ifdef _WIN32
# define API __declspec(dllexport)
#else
# define API
#endif
API char* myfunc(void *mybuffer, int buflen) {
const uint8_t* tmp = (const uint8_t*)mybuffer;
for(int i = 0; i < buflen; ++i) // show the passed bytes
printf("%02X\n", tmp[i]);
return "output"; // static string no deallocation required
}
test.py
import ctypes as ct
import os
dll = ct.CDLL('./test')
dll.myfunc.argtypes = ct.c_void_p, ct.c_int
dll.myfunc.restype = ct.c_char_p
buf = bytes([1,2,0,0xaa,0x55]) # including embedded null
ret = dll.myfunc(buf, len(buf))
print(ret)
Output:
01
02
00
AA
55
b'output'
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