[Swig-user] How to set attribute from Python to a SWIG wrapped C++ class expecting unsigned char*

[Marcello V. <mar...@it...>]

I am using SWIG 1.3.40 for wrapping C++ code to Python ('swig -c++ 
-python') on RHEL 6.1

In the C++ code, a wrapped class - say Foo - declares an attribute 'ptr' 
as 'unsigned char * ptr' . 
This one I cannot change (it is code generated by yet another tool)

The SWIG generated Foo Python class includes set/get methods for the 'ptr' 
attribute as for all others. 

In the actual use of this code I need (from Python) 
        - to allocate an area and fill it with some binary content 
        - create an instance of the Foo class
        - set the 'ptr' attribute in this object in a way which causes the 
wrapped C++ object to get an 'unsigned char *' pointer to the above area

Having read the SWIG documentation, and wishing to avoid typemaps, I tried 
to get away with malloc(), and memmove() functions to fill-in a buffer of 
unsigned bytes. 
I asked SWIG to generate allocators for unsigned char, namely specifying 
the following in the input file

<mymodule.i>
%include cmalloc.i

%allocators(unsigned char, uchar)

The initial task in the Python exploiting code was to allocate an array 
with binary content and create an instance of  Foo, which I did as follows 
without problems 

<Python code>
import mymodule
from array import array
a = array('B', [(i % 256) for i in range(1024)]
b = mymodule.Foo()

The second task I would like to accomplish as follows

blob = mymodule.malloc_uchar(1024)
mymodule.memmove(blob, a.tostring(), 1024);
b.ptr = blob
... do some work with b ...
mymodule.free_uchar(blob)

Unfortunately, the memmove() function fails with errors: >>> TypeError: in 
method 'memmove', argument 2 of type 'void const *' 

It seems I am stuck here because of memmove() requiring a 'void const *' 
type for its second argument. 
This is different from what is in the 1.3 doc manual at 8.2.4 (pag 110) 
where the 2nd arg is said to be 'char *',
BTW (the manual also declares memmove to take 2 args while it requires 3, 
but that was also reported by other users...)

Is there another way to fill the blob area with the content of array a? 

Any help will be greatly appreciated (Anybody posting a reply on this 
forum, pls give me also an email alert)
___________________________________________
Marcello Vitaletti - mar...@it...