Re: [ctypes-users] Standards for having strings modified by called functions (and structures)?

[Thomas H. <th...@py...>]

"Mark McMahon" <mar...@eu...> writes:

> Hi,
>
> I have had a quick look at Venster (comdlg.py), the ctypes documentation
> (tutorial for version 6.2a), and various other stuff to see if there is
> a reasonably standard way to get text from functions (and filled in
> structures passed to functions).
>
> The easiest way seems to be (but the ctypes tutorial gives me the
> impression it might be unsafe because python strings are immutable!)
> 	# make the string big enough for the text 
> 	#(including nul terminator usually - but depends on the
> data/function)
> 	myString = '\0'* lenghtOfString    # STEP 1
>
> 	# call the function, myString is modified
> 	FunctionModifyingString(myString)    # STEP 2
>

Right, Python strings are immutable. In C code, it's impossible to
enforce this (unless you use the 'const' attribute).
Although I cannot provide an example, I guess all hell breaks lose if
you use ctypes (or C code) which violates this. And ctypes doesn't
(yet?) have a const sttribute.

Thomas

> P.S. If you install Py2exe or ctypes you don't get the documentation -
> can that be installed aswell?

For both, it's included in the source distro. But installing it maybe
useful.