std::map - erase+continue

[Gernot Frisch]

restart:
for (std::map<x,y>: :iterator it = m.begin(); it!=m.end(); ++it)
{
if( it->second.isbad () )
{
std::map<x,y>:: iterator next = it;
++next;
m.erase(it);
it=next;
// goto restart;
}
}

this does not remove all bad ones... If I insert a "goto restart" it
works...

What am I doing wrong?
--
-Gernot
int main(int argc, char** argv) {printf
("%silto%c%cf%c gl%ssic%ccom%c" , "ma", 58, 'g', 64, "ba", 46, 10);}

[Gernot Frisch]

This version hangs by the thinnest of threads, but it does still
work.

I do not understand what you mean. :?

[Gernot Frisch]

"Gernot Frisch" <[e-mail] > schrieb im Newsbeitrag
news:39******** *****@individua l.net...

This version hangs by the thinnest of threads, but it does still
work.

I do not understand what you mean. :?

I _do_ understand now, but I don't understand how it can be working
now ;)

m.erase(it++); is the same as:
m_erase(it); it++;
right?
But after deleting at 'it', I can't '++' it anymore, can I? Does the
std say so?

[Kamil Burzynski]

On Tue, 8 Mar 2005 17:19:42 +0100
"Gernot Frisch" <[e-mail] > wrote:

m.erase(it++); is the same as:
m_erase(it); it++;
right?
But after deleting at 'it', I can't '++' it anymore, can I? Does the
std say so?

No, it is rather like this:

SomeIiterator tmp = it;
++it;
m.erase(tmp);

There is sequence point before erase() call, so it is already
incremented before call starts. Additionally, the erase() call gets old
(i.e. non-incremented) value as an argument.

--
Best regards from
Kamil Burzynski

[Andre Kostur]

> map/multimap/set/multiset are based on tree structures and they

allocate when you call insert and free when you call erase/clear. So
they don't have a member function like resize() as in list/vector.

list has a resize?! Oh wait.. resize(), not reserve(). I think the OP was
more concerned as to whether list keeps "dead" nodes around (ie: if you
erase() an element from the list, does the capacity() (assuming list had a
capacity() member) remain constant, or does it go down by 1). No, list
doesn't keep dead nodes around. (Is that mandated by Standard, I'm not
sure).

[Gernot Frisch]

"Andre Kostur" <nn******@kostu r.net> schrieb im Newsbeitrag
news:Xn******** *************** ********@207.35 .177.135...

map/multimap/set/multiset are based on tree structures and they
allocate when you call insert and free when you call erase/clear.
So
they don't have a member function like resize() as in list/vector.

list has a resize?! Oh wait.. resize(), not reserve(). I think the
OP was
more concerned as to whether list keeps "dead" nodes around (ie: if
you
erase() an element from the list, does the capacity() (assuming list
had a
capacity() member) remain constant, or does it go down by 1). No,
list
doesn't keep dead nodes around. (Is that mandated by Standard, I'm
not
sure).

Actually my question was: will pointers to other elements stay when I
remove/insert an element. (vector won't, list will keep pointers
valid)
-Gernot

[Peter Gordon]

"Gernot Frisch" <[e-mail] > wrote in news:397qcfF5uq 1i4U1
@individual.net :

Actually my question was: will pointers to other elements stay when I
remove/insert an element. (vector won't, list will keep pointers
valid)
-Gernot

Are you sure? In the following code fragment:

list::iterator itr;
list mylist;
for(itr = mylist.begin(); itr != mylist.end(); ++itr) {
// delete the last elemant in the list
}

What happens to the "itr != mylist.end()" test?

BTW, I'm not being smart, I don't know, but suspect
that it is highly compiler dependent.

[Gernot Frisch]

>> Actually my question was: will pointers to other elements stay when

I
remove/insert an element. (vector won't, list will keep pointers
valid)
-Gernot

Are you sure? In the following code fragment:

list::iterator itr;
list mylist;
for(itr = mylist.begin(); itr != mylist.end(); ++itr) {
// delete the last element in the list
}

What happens to the "itr != mylist.end()" test?

BTW, I'm not being smart, I don't know, but suspect
that it is highly compiler dependent.

What I meant is:

X* pX = &mylist.first() ;
mylist.push_bac k(some_X); // Add some more data
mylist.erase(++ mylist.begin() ); // Remove the 2nd item

pX -> DoSomething(); // valid if 'mylist' is std::list, propably
invalid it it's std::vector

-Gernot

[Andre Kostur]

Peter Gordon <petergo@_delet eme_.netspace.n et.au> wrote in
news:Xn******** *************** ***********@203 .10.110.105:

"Gernot Frisch" <[e-mail] > wrote in news:397qcfF5uq 1i4U1
@individual.net :

Actually my question was: will pointers to other elements stay when I
remove/insert an element. (vector won't, list will keep pointers
valid)
-Gernot

Are you sure? In the following code fragment:

list::iterator itr;
list mylist;
for(itr = mylist.begin(); itr != mylist.end(); ++itr) {
// delete the last elemant in the list
}

What happens to the "itr != mylist.end()" test?

mylist.end() points to the one-past-the-end element. In this particular
case, it doesn't really matter since .end() is reevaluated every time you
go through the loop.

Nitpick, if you happen to be on the last element when you delete the last
element in the list, this loop will exhibit undefined behaviour since when
you delete the last element, the itr variable becomes an invalidated
iterator. Then you try to increment it, which is undefined behaviour.