Question

currently I am trying to understand how to move an element in Boost::ptr_list to the front.

I have been trying stuff like this:

boost::ptr_list<myObj> mylist;
boost::ptr_list<myObj> myiter;
// Do something useful
mylist.transfer(mylist.begin(), myiter, mylist);

This version the compiler acccepts, but my program crashes on the first call to transfer.

Another thing I tried was

mylist.push_front(mylist.release(myiter));

This the compiler rejects due to incompatible types.

What am I doing wrong? Thanks for your help.

Answer 1

I am assuming here you want to move the last element in the list to the front. If so here is one possible way to do it:

struct myObj 
{
    myObj( int i ) : m_i(i)
    {

    }

    void print() const
    {
        std::cout << "i == " << m_i << std::endl;
    }

private:

    int m_i;
};

typedef boost::ptr_list<myObj> tMyList;

void PrintList( const tMyList& list )
{
    std::cout << "List contains: " << std::endl;

    tMyList::const_iterator itEnd = list.end();
    for (tMyList::const_iterator it = list.begin(); it != itEnd; ++it )
    {
        it->print();
    }
}

void test()
{
    tMyList mylist;

    mylist.push_back(new myObj(1));
    mylist.push_back(new myObj(2));
    mylist.push_back(new myObj(3));

    PrintList(mylist);

    //move last element to the front
    tMyList::auto_type pBack = mylist.pop_back();
    mylist.push_front( pBack.release() );

    PrintList(mylist);
}

int main() 
{ 
    test();
    return 0;
}