compare pointers in std::list

std::find(testList.begin(),testList.end(),ObjA) == testList.end()

The above is true if the object ObjA cannot be found in the list.

Quote:

Original post by Risto Hietanen Hi all, Suppose the following: I have 3 instances of a class CSimpleClass: CSimpleClass* ObjA = new CSimpleClass; CSimpleClass* ObjB = new CSimpleClass; CSimpleClass* ObjC = new CSimpleClass; I then add the pointers to these classes to a list: std::list testList; testList.push_back( ObjA ); testList.push_back( ObjB ); testList.push_back( ObjC ); The list now contains copies of the pointers to the objects. Now, suppose I want to check if ObjA is present in the list, what would be the best way to do this (without using an unique id of each class)? Best Regards, Risto

Couldn't you just do this:

if( std::find( testList.begin(), testList.end(),ObjA ) != testList.end() ){  std::cout << "ObjA is in the list\n";}

Or are you talking about checking for the (*ObjA)? Then you could do this:

for( std::list<CSimpleClass*>::const_iterator iter = testList.begin();iter != testList.end();++iter){  if( **iter == *ObjA )  {    std::cout << "*ObjA is in the list\n";    break;  }}

A pointer does not "point to an address". It is an address. Now, the question is: do you want to remove any object equal to the passed object, or do you want to remove the passed object itself?

In the first case, you merely have to use std::find, which returns an iterator which you can then list.erase() to have it removed. Even simpler: you can use list.remove() to remove the object without even checking that it's there.

In the second case, you have to actually traverse the entire list to compare the objects pointed to with the passed object.

---

Simple clarification:

int a = 10;
int b = 10;

a and b are equal, but are not the same object. This means that you can change one without changing the other. In the following case:

int a = 10;
int *b = &a
int *c = &a

Then a, *b and *c are the same object, and b == c.

I want to remove the passed object from the list so that the event manager does not call the listener if it ha unregistered from the list.

So then I should do something like this:

*********************
bool UnRegister(CEventListener* listener)
{
if (listener == NULL)
{
return false;
}

for( m_It = m_Listeners.begin(); m_It != m_Listeners.end(); ++m_It)
{
if( **m_It == *listener )
{
CEventListener* tmpListener = (*m_It);
SAFE_DELETE(tmpListener);
m_Listeners.erase(m_It);
return true;
}
}
return false;
}

*******************

Your code removes the first object in the list that is equal to the passed object. Others may remain.

Thanks a lot for Your help ToohrVyk!
Now I think I understand how it works.

/Best Regards,
Risto