c++ , python -- seg fault , I miss something

DrakeMagi · March 2010

using Swig - getting segmentation fault.

but not all the time. I thought i had it working until i change my list.

my c++ version works fine. so must have to do with python api ,

something i misunderstood or forgot.

my Qsort.cpp

// QuickSort
// written in c++

#include <iostream>
#include "/usr/include/python2.5/Python.h"
#include "Qsort.hpp"

int count = 0;

void Swap( PyObject *array , int a , int b )
{
count++;
PyObject *c = PyList_GetItem(array , a);
PyObject *d = PyList_GetItem(array , b);

if (PyList_SetItem(array , a , d ))
{ std::cout << "Failed" << std::endl; }
if (PyList_SetItem(array , b , c ))
{ std::cout << "Failed" << std::endl; }

}

int Partition( PyObject *array , int left , int right , int pivot)
{
PyObject *checkvalue , *pivotvalue;
pivotvalue = PyList_GetItem(array , pivot);
Swap ( array , pivot , right );
int storeindex = left;
for ( int i = left; i < right; i++ )
{
checkvalue = PyList_GetItem(array , i);
if ( PyObject_RichCompareBool( checkvalue , pivotvalue , Py_LE ) )
{
Swap ( array , i , storeindex );
storeindex++;
}
}
Swap ( array , storeindex , right );
return storeindex;
}

void Quicksort ( PyObject *array , int left , int right )
{
int pivot;
if ( right > left )
{
pivot = (left + right) / 2;
pivot = Partition( array , left , right , pivot );
Quicksort( array , left , pivot - 1 );
Quicksort( array , pivot + 1 , right );
}
}

PyObject *Qsort ( PyObject *List )
{
int List_size;
List_size = PyList_Size( List );
Quicksort( List , 0 , List_size-1 );
std::cout << count << std::endl;
return List;
}

my Qsort.hpp

#ifndef QSORT_PY
#define QSORT_PY

PyObject *Qsort ( PyObject *List );

#endif

my Qsort.i

/* Qsort C++ , Python */

%module Qsort

%{
#define SWIG_FILE_WITH_INIT
#include "Qsort.hpp"
%}

PyObject *Qsort ( PyObject *List );

my python make file

import commands

print commands.getstatusoutput( 'swig -c++ -python Qsort.i' )
print commands.getstatusoutput( 'g++ -O2 -fPIC -c Qsort.cpp' )
print commands.getstatusoutput( 'g++ -O2 -fPIC -c Qsort_wrap.cxx -I/usr/include/python2.5' )
print commands.getstatusoutput( 'g++ -shared Qsort.o Qsort_wrap.o -o _Qsort.so' )

DrakeMagi · March 2010

figure my segmentation fault is from reference in python.
Now i trying to figure out how to use them.

void Swap( PyObject *array , int a , int b )  
{ 
    count++; 
    PyObject *c = PyList_GetItem(array , a);  
    PyObject *d = PyList_GetItem(array , b); 
    Py_XINCREF(c); Py_XINCREF(d); // had to made them there own reference ?
     
    if (PyList_SetItem(array , a , d )) 
    { std::cout << "Failed" << std::endl; } 
    if (PyList_SetItem(array , b , c )) 
    { std::cout << "Failed" << std::endl; } 
 
}

Trying to figure out which one to use and where and why ?
Py_DECREF , Py_INCREF , Py_XDECREF , Py_XINCREF

Seems like i fix it. But not 100% sure.

c++ , python -- seg fault , I miss something

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