Re: Question about strings and pointers

* Valentin Haenel <[email protected]> [100220]:
> * Ananda Regmi <[email protected]> [100208]:
> > Try this to create the ctypes string in python and then pass pointer  with
> > your function call.
> > 
> > import ctypes
> > temp_str = 'this is the substring we would like to print'
> > my_string = ctypes.create_string_buffer(temp_str, len(temp_str))
> 
> O.k. and how would i obtain pointers into the buffer? for example my_string[12]
> again returns an object of type str.

Well then, after playing with it for a while now, i have a working solution, not
exactly elegant, but it works. The idea of using a string_buffer was a pretty
good start.

The trick i used is to specify the argument types of the c function as c_int
instead of POINTER(c_char). I can then use 'addressof' to obtain the location in
memory of the string (in fact a pointer to the first character of the string).
Lastly i used multiples of sizeof(int) to index into the string_buffer.

code is attached.

V-

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from ctypes import *
lib = cdll.LoadLibrary('./libdemo-library.so.1')
lib.print_substring.argtypes = [c_int, c_int]
test = "this is the substring we would like to print"
test_buf = create_string_buffer(test, len(test))
add = addressof(test_buf)
lib.print_substring(add+12*sizeof(c_char), add+21*sizeof(c_char))