passing strings to ctypes functions under Python 3.x

Question

from ctypes import *
msvcrt = cdll.msvcrt
message_string = "Hello world!\n"
msvcrt.printf("Testing: %s", message_string)

I'm going through a book about Ctypes and Python but the example code just doesn't work.

Could it be because the book was written for python 2 whereas I am on Python 3?

printf is only printing the first letter.

Answer 1

The C printf function is expecting byte strings. In Python 3 all strings are unicode so you'll have to encode to bytes:

>>> msvcrt.printf("Testing: %s".encode('ascii'), message_string.encode('ascii'))
Testing: Hello world!
22

If you have any non-ascii characters then encode to the relevant windows codepage instead.

Answer 2

bleh, using "".encode('ascii') is ugly. You can often get away with just doing this:

TTF_OpenFont(b"assets/droid.ttf", 10)
             ^^

Note the 'b' type for the string. This is portable to python 2.7 as well.