Calling a C function with a b"..." string parameter

Question

from ctypes import *
libc = CDLL("/lib/x86_64-linux-gnu/libc/so/6")
libc.printf(b"Hello world")

I was studying the library ctypes in Python. In above printf function why do we use b before "Hello world"?

Answer 1

The b"..." notation represents a byte string. Byte strings are immutable are appropriate for passing to const char * C function parameters, or char * if the function is known not to write to the string. Use ctypes.create_string_buffer() if you need a writeable buffer.