loop for and std::list iterator

[raven.mp4]

Hi,
I have a little question about std::list iterators. Take a look at
this piece of code:

list<Type*>::iterator it = myList.begin();

Type *p;

for(it; it != myList.end(); ++it)
{
p = (*it);

if(...)
{
myList.pop_front();
InsertIntoList(p); // inserts p into new location
it = myList.begin();
}
else
break;
}

Why 'it = myList.begin()' doesn't set 'it' to the beginning of the
myList?

 

[Markus Schoder]

Hi,
I have a little question about std::list iterators. Take a look at this
piece of code:

list<Type*>::iterator it = myList.begin();

Type *p;

for(it; it != myList.end(); ++it)
{
p = (*it);

if(...)
{
myList.pop_front();
InsertIntoList(p); // inserts p into new location
it = myList.begin();
}
else
break;
}

Why 'it = myList.begin()' doesn't set 'it' to the beginning of the
myList?

It does. Then "it" gets incremented (possibly invoking undefined
behaviour if the list is empty) and then the next loop iteration begins
with "it" pointing to the second element in the list.

It is difficult to tell but it almost looks like you rather wanted

while(!myList.empty())
{
it = myList.begin();
p = *it;

if(...)
{
myList.pop_front();
InsertIntoList(p); // inserts p into new location
}
else
break;
}

 

[raven.mp4]

It does. Then "it" gets incremented (possibly invoking undefined
behaviour if the list is empty) and then the next loop iteration begins
with "it" pointing to the second element in the list.

It is difficult to tell but it almost looks like you rather wanted

while(!myList.empty())
{
it = myList.begin();
p = *it;

if(...)
{
myList.pop_front();
InsertIntoList(p); // inserts p into new location
}
else
break;

}

Oh, now I see my mistake. Thank you for explanation.