#include <iostream>
using std::cout;
using std::endl;
#include <list>
#include <algorithm>
#include <afxwin.h>
#include <fstream>
using std::ostream;
using std::istream;
using std::ofstream;
using std::list;
using std::fstream;
using std::ios;
#define SIZE 5
class Example
{
public:
Example() {}
Example(int Value, bool bDead = false) {value = Value; dead = bDead;}
int getValue() {return value;}
void setValue(int newValue) {value = newValue;}
bool dead;
private:
int value;
};
//typedef for easier readability
typedef list<Example *> ExampleList;
typedef list<Example *>::iterator exItor;
void printList(std::list< Example * > &listRef);
void saveList(std::list< Example * > &listRef, char* filename);
void loadList(std::list< Example * > &listRef, char* filename);
void main()
{
ExampleList theList; //list of example classes
ExampleList secondList;
Example* ptr;
//Populate the list
// loadList(theList, "Example.txt");
theList.push_back(new Example(5));
theList.push_back(new Example(4));
theList.push_back(ptr = new Example(3, true));
theList.push_back(new Example(2));
theList.push_back(new Example(1));
secondList = theList;
printList(theList);
list<Example *>::iterator it;
cout << "Deleting dead items:" << endl;
for(it = theList.begin(); it != theList.end(); it++)
{
if((*it)->dead == true)
theList.remove(*it);
}
printList(theList);
cout << "Here''s the second:\n";
printList(secondList);
}
void printList(std::list< Example * > &listRef)
{
if(listRef.empty())
cout << "List is empty.\n";
else
{
// std::ostream_iterator< T > output(cout, " "); //declare output iterator
// std::copy(listRef.begin(), listRef.end(), output); //copy to output stream
std::list< Example * >::iterator it;
for(it = listRef.begin(); it != listRef.end(); it++)
{
cout << (*it)->getValue() << endl;
}
cout << endl;
}
}
Deleting objects in std::list
Author
I''ve been trying to delete objects in std::list, but it never seems to work right.
In the following example, I try to delete all the "dead" objects in a list by looping through them and using remove on the "dead" ones. After deleting the dead object, the next object in the loop causes a crash, as though I were trying to access a NULL pointer.
The loop you're using to remove dead items is error-prone. The problem looks like you're trying increment an invalidated iterator. Instead consider using the std::list::remove_if() member function.
edit: unless you're using MSVC 6 which doesn't properly support the remove_if() member function for std::list objects. In that case you'd need to do something like:
[edited by - SiCrane on March 21, 2004 4:22:22 PM]
edit: unless you're using MSVC 6 which doesn't properly support the remove_if() member function for std::list objects. In that case you'd need to do something like:
for(it = theList.begin(); it != theList.end(); ) { if((*it)->dead == true) { it = theList.erase(it); } else { ++it; } } [edited by - SiCrane on March 21, 2004 4:22:22 PM]
A less elegant but more simple (and erase_if-free) solution might look a bit like...
list<Example*>::iterator thisOne = ExampleList.begin(), max = ExampleList.end(), lastOne = thisOne;lastOne--;while (thisOne != max){ if (*thisOne->dead) { ExampleList.erase(thisOne); thisOne = lastOne; thisOne++; } else { lastOne = thisOne; thisOne++; }}This topic is closed to new replies.
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