STL question

OpenGL OpenGL: User Software
1

I have created a list of class objects.The question is, why doesn’t the following code delete the list items when the condition is fufilled.
The code:

…
list<racheta*> listaRachete;
list<racheta*>::iterator iterIntList;
…

switch(key)
{
case 32 :
racheta *a=new racheta;
listaRachete.push_front(a);
break;
}
…

…
for(iterIntList=listaRachete.begin();iterIntList!=listaRachete.end();iterIntList++) {
if ((*iterIntList)->dead==1) delete *iterIntList;
else
(*iterIntList)->mutaRacheta();}
…

2

The following line of code is dangerous :


if ((*iterIntList)->dead==1) delete *iterIntList;

You delete the memory of the pointer in the STL list but the pointer is still in the list.

I think you can do something like this


for(iterIntList=listaRachete.begin();iterIntList!=listaRachete.end();iterIntList++) {
if ((*iterIntList)->dead==1)
{ 
 delete *iterIntList;
 listaRachete.erase(iterIntList);
}
else
{
(*iterIntList)->mutaRacheta();}
}

I have not tested so I hope that it will not segfault.

3

The code doesn’t work.Thank you for trying altought.

4

As previously mentioned you deleted the object that is still within the list. One suggestion, take a look at the boost library and it’s smart pointer(like shared_ptr). shared_ptr deletes the object for you when reference count drops to 0. Then you can do

typedef boost::shared_ptr<racheta> pracheta;
std::list<pracheta> listaRachete;
...
listaRachete.push_front(pracheta(new racheta));
...

As for deleting object from list. A proper way of doing this would be like this:


...
class ErasePred
{
    public:
    bool operator()(prachete r) const
    {
        if (r->dead == 1)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
};
...
// remove all elements for which 
// ErasePred::operator() returns true
std::remove_if(listaRachete.begin(), 
               listaRachete.end(), 
               ErasePred());

…of the top of my head.

5

There seems to be an error with the declaration of class ErasePred…

6

The problem with my code is after this instruction listaRachete.erase(iterIntList); I cannot use the iterIntList iterator anymore to advance in the list.

The following use 2 iterators:


list<racheta*>::iterator iterIntList;
list<racheta*>::iterator deleteIntList;

iterIntList = iterIntList=listaRachete.begin();
while(iterIntList!=listaRachete.end())
{
  if ((*iterIntList)->dead==1)
  {
   deleteIntList =  iterIntList;
   iterIntList++;
   delete *deleteIntList;
   listaRachete.erase(deleteIntList);
  }
  else
  {
   (*iterIntList)->mutaRacheta();}
   iterIntList++;
  }

}

I have tested that and it work.

7

Thank you very much for the help.You helped allot.