how to get raw bytes for ctypes functions that return c_wchar_p

Thomas Heller theller at ctypes.org
Tue Nov 19 18:22:36 CET 2013


Am 19.11.2013 17:58, schrieb Mark Summerfield:
> Hi,
>
> I am using ctypes to access a function in a DLL using Python 3.3
> 32-bit on Windows 7 64-bit:
>
> dplGetPageText = dpl.DPLGetPageText dplGetPageText.argtypes =
> (ctypes.c_int, ctypes.c_int) dplGetPageText.restype =
> ctypes.c_wchar_p
>
> Python returns this as a str with the raw bytes already decoded.
>
> Unfortunately, when the returned text contains some special
> characters (e.g. © or fi) it is not encoded correctly. This may be a
> problem with Windows or with ctypes or with the library I'm using; or
> of course, it could be my own mistake.
>
> To find out, I'd like to change the restype to give me the raw bytes
> so that I can view them and if necessary decode them myself.
>
> Can anyone tell me how to change the restype to get the bytes?

ctypes on Python 2.7 has the set_conversion_mode(coding, errors)
which could be used to change the way c_wchar_p is converted
from/to Python strings.
Unfortunately it seems to be gone in Python 3.3.

However, you can set restype to POINTER(c_char) and then
index the result:

result = dplGetPageText(...)
print(result[0], result[1], result[2])

Thomas



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