Hi i'm relatively new to Python and my C/C++ knowledge is near to
None. Having said that I feel justified to ask stupid questions :)
Ok now more seriously. I have question refering to char* used as
function parameters to return values. I have read SWIG manual to find
best way to overcome that, but there are many warnings about memory
leaks and stuff, so I feel confused.
Ok to put it more simply: how to safely define a variable in Python
and have it modified by C/C++ function?
Even better would be a way to make a tuple of return value and out
parameters, but thats probably a lot more work.
Any hint will be appreciated! 3 2121
Am Dienstag, 29. Juli 2008 12:51:36 schrieb code_berzerker:
Ok now more seriously. I have question refering to char* used as
function parameters to return values. I have read SWIG manual to find
best way to overcome that, but there are many warnings about memory
leaks and stuff, so I feel confused.
Ok to put it more simply: how to safely define a variable in Python
and have it modified by C/C++ function?
At least for strings, this won't work. Python strings are immutable (and
Python optimizes some things based on this knowledge), and as such you can
pass a Python string(-object) into a C/C++ function and retrieve its value
there as a const (!) char* using the PyString_*-API (I have no idea how this
is encapsulated in SWIG), but cannot/should not modify it (a const_cast<is
almost always a sign of bad programming, anyway).
The only real choice you have is to have your wrapper return a new string
object, created using one of the PyString_FromSt ring[AndSize] functions.
Check the Python C-API documentation for more info on this.
Anyway, on a different note, I personally have always found it simpler to not
use SWIG to generate C extensions for Python, but to use the Python C-API
directly.
Hope this helps!
--
Heiko Wundram
Ok I think I got it:
PyObject* myFuncXXX(char* p_1, int p_2, char* p_3, int p_4)
{
int res;
char _host[255] = "";
int _port;
res = funcXXX(p_1, p_2, p_3, p_4, _host, &_port);
PyObject* res1 = PyInt_FromLong( res);
PyObject* res2 = PyString_FromSt ringAndSize(_ho st, strlen(_host));
PyObject* res3 = PyInt_FromLong( _port);
PyObject* resTuple = PyTuple_New(3);
PyTuple_SetItem (resTuple, 0, res1);
PyTuple_SetItem (resTuple, 1, res2);
PyTuple_SetItem (resTuple, 2, res3);
return resTuple;
}
It seems to work when I put it into swig's "*.i" file.
me proud of me.self :D
code_berzerker wrote:
Hi i'm relatively new to Python and my C/C++ knowledge is near to
None. Having said that I feel justified to ask stupid questions :)
Have you considered using Cython? It's almost Python, but it compiles to C
code for a Python extension module and even lets you call C functions directly
from your code. http://cython.org/
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