Trouble creating char * object to send to c++/c shared object library

Question

First off I am new to ctypes and did search for an answer to my question. Definitely will appreciate any insight from here.

I have a byte string supplied to me by another tool. It contains what appears to be hex and other values. I'm creating the c_char_p object as follows:

mybytestring = b'something with a lot of hex \x00\x00\xc7\x87\x9bb and other alphanumeric and non-word characters'     # Length of this is very long let's say 480
mycharp = c_char_p(mybytestring)

I also create a c_char_Array as follows:

mybuff = create_string_buffer(mybytestring)

The problem is when I send either mycharp or mybuff to a c++ library .so function, the string gets cut off at the NULL terminator (first occurrence of '\x00')

I'm loading the c++ library and calling the function as follows:

lib_handle = cdll.LoadLibrary(mylib.so)
lib_handle.myfunction(mycharp)
lib_handle.myfunction(mybuff)

The c++ function expects a char *

Does someone know how to be able to send the whole string with NULL terminators ('\x00') included?

Thanks

Thanks. He had to make change on his side to handle the data correctly. — Derek N
– Derek N, Commented Apr 19, 2013 at 18:23

qPCR4vir · Accepted Answer · 2013-04-12 07:32:06Z

2

Add your original data to a vector<char> vec, and send vec.data()

But the actual problem is

The c++ function expects a char *.

You will need to change this (to accept a second arg=length of the buffer, or for example, to accept a vector<char>) if you want it to accept an array of char including null.

Alternatively you can figure out what do you actually want the c++ function to do, and make self a "preprocessing" of the char array, adding a null-terminator to each new array, and after that send to the c++ function.

For example, you may decide that the “input” array is actually a set of c-string: you will need to do a simple parse to “split” and send to the c++ in a cycle one, after other.

Or maybe you decide that the input could be a string in an UTF16 and not UTF8. Then you need to, as good as possible, convert it to UTF8 and send to the c++ function.

edited Apr 12, 2013 at 7:32

answered Apr 12, 2013 at 6:35

qPCR4vir

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1 Comment

Derek N Over a year ago

Thanks for the tip. It turned out the other developer's c++ library was not handling the data correctly.

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