Question

I have a vector of pointers to a class. I need to call their destructors and free their memory. Since they are vector of pointers vector.clear() does not do the job.So I went on to do it manually like so :

void Population::clearPool(std::vector<Chromosome*> a,int size)
{
    Chromosome* c;
    for(int j = 0 ;j < size-1;j++)
    {
       c = a.back();
       a.pop_back();
       delete c;
       printf("  %d \n\r",j);
       c = NULL;

    }

}

The printf in there is since I have a talking destructor to see in which Chromosome the segmentation fault happens. When clearPool() is called and say we got a size of 100, it can give a segmentation fault in any Chromosome between 0 and 100.

I have no idea why this might be happening nor do I have a way to actually find what’s wrong since while debugging with breakpoints all I see is that it happens in there at random chromosomes.

I am using codeblocks IDE and the gdb debugger. The stack trace when the segmentation fault happens has 4 memory addresses and a function wsncpy().

Answer 1

void Population::clearPool( std::vector <Chromosome*> & a )
{
   for ( int i = 0; i < a.size(); i++ ) {
      delete a[i];
   }
   a.clear();
}

Notice that the vector is passed by reference. In your code, a copy of the vector is used, which means that it is unchanged in the calling program. Because you delete the pointers in the copy, the pointers in the original are now all invalid – I suspect you are using those invalid pointers in some way not shown in the code you posted.

As a couple of template solutions have been posted that use C++ library algorithms, you might also want to consider a template solution that does not:

template <class C> void FreeClear( C & cntr ) {
    for ( typename C::iterator it = cntr.begin(); 
              it != cntr.end(); ++it ) {
        delete * it;
    }
    cntr.clear();
}

Using this you can free any container of dynamically allocated objects:

vector <Chromosome *> vc;
list <Chromosome *> lc;
// populate & use
FreeClear( lc );
FreeClear( vc );