how to get raw bytes for ctypes functions that return c_wchar_p

Mark Summerfield list at qtrac.plus.com
Tue Nov 19 19:58:32 CET 2013


On Tuesday, November 19, 2013 5:22:36 PM UTC, Thomas Heller wrote:
> 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

That worked well. I also tried POINTER(c_wchar) which also worked (but in a different way). Now I can see the raw bytes and decode them how I like.

Thanks!



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